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| ac SEPTEMBER 2003 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO REV. 1.0.0 GENERAL DESCRIPTION The XR16L25501 (L2550) is a dual universal asynchronous receiver and transmitter (UART). The XR16L2550 is an improved version of the ST16C2550 UART with lower operating voltages and 5 volt tolerant inputs. The L2550 provides enhanced UART functions with 16 byte FIFOs, a modem control interface and data rates up to 4 Mbps. Onboard status registers provide the user with error indications and operational status. System interrupts and modem control features may be tailored by external software to meet specific user requirements. Independent programmable baud rate generators are provided to select transmit and receive clock rates up to 3.125 Mbps. The Baud Rate Generator can be configured for either crystal or external clock input. An internal loopback capability allows onboard diagnostics. The L2550 is available in a 44-pin PLCC, 48-pin TQFP and 32-pin QFN packages. The L2550 is fabricated in an advanced CMOS process. NOTE: 1 Covered by U.S. Patent #5,649,122. FEATURES * 2.25 to 5.5 Volt operation * 5 Volt tolerant inputs * Pin-to-pin compatible to Exar's ST16C2450, ST16C2550 and XR16L2750 in 44-PLCC and 48TQFP packages * Pin-to-pin compatible to XR16C2850 in 44-PLCC * Pin alike XR16L2551, XR16L2751 and XR16C2850 in 48-TQFP package * Two independent UART channels s s s Up to 3.125Mbps with external clock of 50 MHz Register Set compatible to 16C550 16 byte Transmit FIFO to reduce the bandwidth requirement of the external CPU 16 byte Receive FIFO with error tags to reduce the bandwidth requirement of the external CPU 4 selectable Receive FIFO interrupt trigger levels Automatic RTS/CTS hardware flow control Automatic Xon/Xoff software flow control Wireless infrared encoder/decoder Full Modem Interface (CTS#, RTS#, DSR#, DTR#, RI#, CD#) Programmable character lengths (5, 6, 7, 8) with even, odd, or no parity s s APPLICATIONS s s s s * Portable Appliances * Medical Monitors * Base Stations * Micro Servers * Telecommunication Network Routers * Industrial Automation Controls FIGURE 1. XR16L2550 BLOCK DIAGRAM s * Tiny 32-QFN, no lead package (5x5x0.9mm) * 44-PLCC and 48-TQFP packages also available A2:A0 D7:D0 IOR# IOW# CSA# CSB# INTA INTB TXRDYA# TXRDYB# RXRDYA# RDRXYB# Reset 8-bit Data Bus Interface * 5 Volt Tolerant Inputs 2.25 to 5.5 Volt VCC GND UART Channel A UART Regs BRG 16 Byte TX FIFO TX & RX 16 Byte RX FIFO TXB, RXB, DTRB#, DSRB#, RTSB#, CTSB#, CDB#, RIB#, OP2B# XTAL1 XTAL2 TXA, RXA, DTRA#, DSRA#, RTSA#, DTSA#, CDA#, RIA#, OP2A# UART Channel B (same as Channel A) Crystal Osc/Buffer Exar Corporation 48720 Kato Road, Fremont CA, 94538 * (510) 668-7000 * FAX (510) 668-7017 * www.exar.com XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO FIGURE 2. PIN OUT ASSIGNMENT TXRDYA# DSRA# ac REV. 1.0.0 VCC CTSA# 38 RIA# CDA# 48 45 43 42 41 40 47 46 44 39 37 NC D4 D3 D2 D1 D0 D5 D6 D7 RXB RXA TXRDYB# TXA TXB OP2B# 1 2 3 4 5 6 7 8 9 36 35 34 33 RESET DTRB# DTRA# RTSA# OP2A# RXRDYA# INTA INTB A0 A1 A2 XR16L2550 48-pin TQFP 32 31 30 29 28 27 26 25 CSA# 10 CSB# 11 NC 12 15 13 18 19 20 22 16 14 17 21 23 24 D1 31 D4 D3 32 D5 30 29 28 D2 27 D0 NC 26 RXRDYB# XTAL2 DSRB# RTSB# CTSB# XTAL1 CDB# IOW# IOR# RIB# GND NC 25 CTSA# VCC D6 D7 RXB RXA TXA 1 2 3 4 5 6 7 8 GND 13 IOR 14 # RTSB# 15 10 11 12 16 9 XR16L2550 32-pin QFN 24 RESET 23 RTSA# 22 INTA 21 INTB 20 A0 19 A1 18 17 A2 NC TXRDYA# DSRA# TXB CTSA# CDA# RIA# VCC D4 D3 D2 D1 D0 CSA# CSB# 39 38 37 36 RESET 44 43 42 41 D5 D6 D7 RXB RXA TXRDYB# TXA TXB OP2B# CSA# CSB# 7 8 9 10 11 12 13 14 15 16 17 XTAL1 18 XTAL2 19 IOW# 20 CDB# 21 GND 22 RXRDYB# 23 IOR# 24 DSRB# 25 RIB# 26 RTSB# 27 CTSB# 28 40 6 5 4 3 2 1 XTAL2 DTRB# DTRA# RTSA# 35 OP2A# XR16L2550 44-pin PLCC 34 33 32 31 RXRDYA# INTA INTB A0 30 A1 29 A2 ORDERING INFORMATION PART NUMBER XR16L2550IL XR16L2550IJ XR16L2550IM PACKAGE 32-Lead QFN 44-Lead PLCC 48-Lead TQFP OPERATING TEMPERATURE RANGE -40C to +85C -40C to +85C -40C to +85C DEVICE STATUS Active Active Active 2 CTSB# XTAL1 IOW# NC ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO PIN DESCRIPTIONS Pin Description NAME 32-QFN PIN # 44-PLCC PIN # 48-TQFP PIN # TYPE DESCRIPTION DATA BUS INTERFACE A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 IOR# 18 19 20 2 1 32 31 30 29 28 27 14 29 30 31 9 8 7 6 5 4 3 2 24 26 27 28 3 2 1 48 47 46 45 44 19 I Address data lines [2:0]. These 3 address lines select one of the internal registers in UART channel A/B during a data bus transaction. Data bus lines [7:0] (bidirectional). IO I Input/Output Read Strobe (active low). The falling edge instigates an internal read cycle and retrieves the data byte from an internal register pointed to by the address lines [A2:A0]. The data byte is placed on the data bus to allow the host processor to read it on the rising edge. Input/Output Write Strobe (active low). The falling edge instigates an internal write cycle and the rising edge transfers the data byte on the data bus to an internal register pointed by the address lines. UART channel A select (active low) to enable UART channel A in the device for data bus operation. UART channel B select (active low) to enable UART channel B in the device for data bus operation. UART channel A Interrupt output. The output state is defined by the user and through the software setting of MCR[3]. INTA is set to the active mode (active high) and OP2A# output to a logic 0 when MCR[3] is set to a logic 1. INTA is set to the three state mode and OP2A# to a logic 1 when MCR[3] is set to a logic 0 (Default). UART channel B Interrupt output. The output state is defined by the user and through the software setting of MCR[3]. INTB is set to the active mode and OP2B# output to a logic 0 when MCR[3] is set to a logic 1. INTB is set to the three state mode and OP2B# to a logic 1 when MCR[3] is set to a logic 0 (Default). IOW# 12 20 15 I CSA# CSB# INTA 7 8 22 16 17 33 10 11 30 I I O INTB 21 32 29 O TXRDYA# - 1 43 O UART channel A Transmitter Ready (active low). The output provides the TX FIFO/THR status for transmit channel A. If it is not used, leave it unconnected. UART channel A Receiver Ready (active low). This output provides the RX FIFO/RHR status for receive channel A. If it is not used, leave it unconnected. RXRDYA# - 34 31 O 3 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO Pin Description NAME TXRDYB# 32-QFN PIN # 44-PLCC PIN # 12 48-TQFP PIN # 6 TYPE O DESCRIPTION ac REV. 1.0.0 UART channel B Transmitter Ready (active low). The output provides the TX FIFO/THR status for transmit channel B. If it is not used, leave it unconnected. UART channel B Receiver Ready (active low). This output provides the RX FIFO/RHR status for receive channel B. If it is not used, leave it unconnected. RXRDYB# - 23 18 O MODEM OR SERIAL I/O INTERFACE TXA RXA 5 4 13 11 7 5 O I UART channel A Transmit Data. If it is not used, leave it unconnected. UART channel A Receive Data. Normal receive data input must idle at logic 1 condition. If it is not used, tie it to VCC or pull it high via a 100k ohm resistor. UART channel A Request-to-Send (active low) or general purpose output. This output must be asserted prior to using auto RTS flow control, see EFR[6], MCR[1] and IER[6]. If it is not used, leave it unconnected. UART channel A Clear-to-Send (active low) or general purpose input. It can be used for auto CTS flow control, see EFR[7] and IER[7]. This input should be connected to VCC when not used. UART channel A Data-Terminal-Ready (active low) or general purpose output. If it is not used, leave it unconnected. UART channel A Data-Set-Ready (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel A Carrier-Detect (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel A Ring-Indicator (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. Output Port 2 Channel A - The output state is defined by the user and through the software setting of MCR[3]. INTA is set to the active mode and OP2A# output to a logic 0 when MCR[3] is set to a logic 1. INTA is set to the three state mode and OP2A# to a logic 1 when MCR[3] is set to a logic 0. This output should not be used as a general output else it will disturb the INTA output functionality. If it is not used at all, leave it unconnected. UART channel B Transmit Data. If it is not used, leave it unconnected. UART channel B Receive Data. Normal receive data input must idle at logic 1 condition. If it is not used, tie it to VCC or pull it high via a 100k ohm resistor. RTSA# 23 36 33 O CTSA# 25 40 38 I DTRA# - 37 34 O DSRA# - 41 39 I CDA# - 42 40 I RIA# - 43 41 I OP2A# - 35 32 O TXB RXB 6 3 14 10 8 4 O I 4 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO Pin Description NAME RTSB# 32-QFN PIN # 15 44-PLCC PIN # 27 48-TQFP PIN # 22 TYPE O DESCRIPTION UART channel B Request-to-Send (active low) or general purpose output. This output must be asserted prior to using auto RTS flow control, see EFR[6], MCR[1] and IER[6]. If it is not used, leave it unconnected. UART channel B Clear-to-Send (active low) or general purpose input. It can be used for auto CTS flow control, see EFR[7] and IER[7]. This input should be connected to VCC when not used. UART channel B Data-Terminal-Ready (active low) or general purpose output. If it is not used, leave it unconnected. UART channel B Data-Set-Ready (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel B Carrier-Detect (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. UART channel B Ring-Indicator (active low) or general purpose input. This input should be connected to VCC when not used. This input has no effect on the UART. Output Port 2 Channel B - The output state is defined by the user and through the software setting of MCR[3]. INTB is set to the active mode and OP2B# output to a logic 0 when MCR[3] is set to a logic 1. INTB is set to the three state mode and OP2B# to a logic 1 when MCR[3] is set to a logic 0. This output should not be used as a general output else it will disturb the INTB output functionality. If it is not used, leave it unconnected. CTSB# 16 28 23 I DTRB# - 38 35 O DSRB# - 25 20 I CDB# - 21 16 I RIB# - 26 21 I OP2B# - 15 9 O ANCILLARY SIGNALS XTAL1 XTAL2 RESET 10 11 24 18 19 39 13 14 36 I O I Crystal or external clock input. Crystal or buffered clock output. Reset (active high) - A longer than 40 ns logic 1 pulse on this pin will reset the internal registers and all outputs. The UART transmitter output will be held at logic 1, the receiver input will be ignored and outputs are reset during reset period. 2.25V to 5.5V power supply. All inputs are 5V tolerant. Power supply common, ground. No Connection. These pins are open, but typically, should be connected to GND for good design practice. VCC GND N.C. 26 13 9, 17 44 22 - 42 17 12, 24, 25, 37 Pwr Pwr Pin type: I=Input, O=Output, IO= Input/output, OD=Output Open Drain. 1.0 PRODUCT DESCRIPTION The XR16L2550 (L2550) provides serial asynchronous receive data synchronization, parallel-to-serial and serial-to-parallel data conversions for both the transmitter and receiver sections. These functions are 5 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 necessary for converting the serial data stream into parallel data that is required with digital data systems. Synchronization for the serial data stream is accomplished by adding start and stop bits to the transmit data to form a data character (character orientated protocol). Data integrity is ensured by attaching a parity bit to the data character. The parity bit is checked by the receiver for any transmission bit errors. The electronic circuitry to provide all these functions is fairly complex especially when manufactured on a single integrated silicon chip. The L2550 represents such an integration with greatly enhanced features. The L2550 is fabricated with an advanced CMOS process. Transmit and Receive FIFOs (16 Bytes each) The L2550 is an upward solution that provides a dual UART capability with 16 bytes of transmit and receive FIFO memory, instead of none in the 16C2450. The L2550 is designed to work with high speed modems and shared network environments, that require fast data processing time. Increased performance is realized in the L2550 by the transmit and receive FIFO's. This allows the external processor to handle more networking tasks within a given time. For example, the ST16C2450 without a receive FIFO, will require unloading of the RHR in 93 microseconds (This example uses a character length of 11 bits, including start/stop bits at 115.2 Kbps). This means the external CPU will have to service the receive FIFO less than every 100 microseconds. However with the 16 byte FIFO in the L2550, the data buffer will not require unloading/loading for 1.53 ms. This increases the service interval giving the external CPU additional time for other applications and reducing the overall UART interrupt servicing time. In addition, the 4 selectable receive FIFO trigger interrupt levels is uniquely provided for maximum data throughput performance especially when operating in a multi-channel environment. The FIFO memory greatly reduces the bandwidth requirement of the external controlling CPU, increases performance, and reduces power consumption. Data Rate The L2550 is capable of operation up to 3.125 Mbps with a 50 MHz clock. With a crystal or external clock input of 14.7456 MHz the user can select data rates up to 921.6 Kbps. Enhanced Features The XR16L2550 integrates the functions of 2 enhanced 16C550 Universal Asynchronous Receiver and Transmitter (UART). Each UART is independently controlled having its own set of device configuration registers. The configuration registers set is 16550 UART compatible for control, status and data transfer. Additionally, each UART channel has automatic RTS/CTS hardware flow control, automatic Xon/Xoff and special character software flow control, infrared encoder and decoder (IrDA ver 1.0), programmable baud rate generator with a prescaler of divide by 1 or 4, and data rate up to 4 Mbps at 5V. The rich feature set of the L2550 is available through internal registers. Selectable receive FIFO trigger levels, selectable TX and RX baud rates, and modem interface controls are all standard features. Following a power on reset or an external reset, the L2550 is functionally and software compatible with the previous generation ST16C2450 and ST16C2550. 6 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.0 FUNCTIONAL DESCRIPTIONS 2.1 CPU Interface The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and write transactions. The L2550 data interface supports the Intel compatible types of CPUs and it is compatible to the industry standard 16C550 UART. No clock (oscillator nor external clock) is required to operate a data bus transaction. Each bus cycle is asynchronous using CS#, IOR# and IOW# signals. Both UART channels share the same data bus for host operations. The data bus interconnections are shown in Figure 3. FIGURE 3. XR16L2550 DATA BUS INTERCONNECTIONS D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 IOR# IOW# UART_CSA# UART_CSB# UART_INTA UART_INTB TXRDYA# RXRDYA# TXRDYB# RXRDYB# UART_RESET D0 D1 D2 D3 D4 D5 D6 D7 A0 A1 A2 IOR# IOW# CSA# CSB# INTA INTB TXRDYA# RXRDYA# TXRDYB# RXRDYB# RESET VCC TXA RXA DTRA# RTSA# CTSA# DSRA# CDA# RIA# OP2A# VCC UART Channel A RS-232 Serial Interface TXB RXB UART Channel B DTRB# RTSB# CTSB# DSRB# CDB# RIB# OP2B# RS-232 Serial Interface GND . 2.2 5-Volt Tolerant Inputs The L2550 can accept up to 5V inputs even when operating at 3.3V or 2.5V. But note that if the L2550 is operating at 2.5V, its VOH may not be high enough to meet the requirements of the VIH of a CPU or a serial transceiver that is operating at 5V. 2.3 Device Reset The RESET input resets the internal registers and the serial interface outputs in both channels to their default state (see Table 13). An active high pulse of at least 40 ns duration will be required to activate the reset function in the device. 2.4 Channel A and B Selection The UART provides the user with the capability to bi-directionally transfer information between an external CPU and an external serial communication device. A logic 0 on chip select pins, CSA# or CSB#, allows the user to select UART channel A or B to configure, send transmit data and/or unload receive data to/from the UART. Selecting both UARTs can be useful during power up initialization to write to the same internal registers, but do not attempt to read from both uarts simultaneously. Individual channel select functions are shown in Table 1. TABLE 1: CHANNEL A AND B SELECT CSA# 1 0 CSB# 1 1 FUNCTION UART de-selected Channel A selected 7 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO TABLE 1: CHANNEL A AND B SELECT CSA# 1 0 CSB# 0 0 FUNCTION Channel B selected Channel A and B selected ac REV. 1.0.0 2.5 Channel A and B Internal Registers Each UART channel in the L2550 has a standard register set for controlling, monitoring and data loading and unloading. The configuration register set is compatible to those already available in the standard single 16C550. These registers function as data holding registers (THR/RHR), interrupt status and control registers (ISR/IER), a FIFO control register (FCR), receive line status and control registers (LSR/LCR), modem status and control registers (MSR/MCR), programmable data rate (clock) divisor registers (DLL/DLM), and a user accessible scratch pad register (SPR). 2.6 DMA Mode The device does not support direct memory access. The DMA Mode (a legacy term) in this document doesn't mean "direct memory access" but refers to data block transfer operation. The DMA mode affects the state of the RXRDY# A/B and TXRDY# A/B output pins. The transmit and receive FIFO trigger levels provide additional flexibility to the user for block mode operation. The LSR bits 5-6 provide an indication when the transmitter is empty or has an empty location(s) for more data. The user can optionally operate the transmit and receive FIFO in the DMA mode (FCR bit-3=1). When the transmit and receive FIFO are enabled and the DMA mode is disabled (FCR bit-3 = 0), the L2550 is placed in single-character mode for data transmit or receive operation. When DMA mode is enabled (FCR bit-3 = 1), the user takes advantage of block mode operation by loading or unloading the FIFO in a block sequence determined by the programmed trigger level. The following table show their behavior. Also see Figure 18 through Figure 23. TABLE 2: TXRDY# AND RXRDY# OUTPUTS IN FIFO AND DMA MODE PINS FCR BIT-0=0 (FIFO DISABLED) FCR BIT-0=1 (FIFO ENABLED) FCR Bit-3 = 0 (DMA Mode Disabled) RXRDY# A/B 0 = 1 byte. 1 = no data. 0 = THR empty. 1 = byte in THR. 0 = at least 1 byte in FIFO 1 = FIFO empty. 0 = FIFO empty. 1 = at least 1 byte in FIFO. FCR Bit-3 = 1 (DMA Mode Enabled) 1 to 0 transition when FIFO reaches the trigger level, or time-out occurs. 0 to 1 transition when FIFO empties. 0 = FIFO has at least 1 empty location. 1 = FIFO is full. TXRDY# A/B 2.7 INTA and INTB Outputs The INTA and INTB interrupt output changes according to the operating mode and enhanced features setup. Table 3 and Table 4 summarize the operating behavior for the transmitter and receiver. Also see Figure 18 through Figure 23. TABLE 3: INTA AND INTB PINS OPERATION FOR TRANSMITTER FCR BIT-0 = 0 (FIFO DISABLED) INTA/B Pin 0 = a byte in THR 1 = THR empty FCR BIT-0 = 1 (FIFO ENABLED) 0 = at least 1 byte in FIFO 1 = FIFO empty 8 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO TABLE 4: INTA AND INTB PIN OPERATION FOR RECEIVER FCR BIT-0 = 0 (FIFO DISABLED) INTA/B Pin 0 = no data 1 = 1 byte FCR BIT-0 = 1 (FIFO ENABLED) 0 = FIFO below trigger level 1 = FIFO above trigger level 2.8 Crystal Oscillator or External Clock Input The L2550 includes an on-chip oscillator (XTAL1 and XTAL2) to produce a clock for both UART sections in the device. The CPU data bus does not require this clock for bus operation. The crystal oscillator provides a system clock to the Baud Rate Generators (BRG) section found in each of the UART. XTAL1 is the input to the oscillator or external clock buffer input with XTAL2 pin being the output. For programming details, see "Programmable Baud Rate Generator." FIGURE 4. TYPICAL OSCILLATOR CONNECTIONS XTAL1 XTAL2 R1 0-120 (Optional) R2 500 - 1 Y1 1.8432 MHz to 24 MHz C1 22-47 pF C2 22-47 pF The on-chip oscillator is designed to use an industry standard microprocessor crystal (parallel resonant, fundamental frequency with 10-22 pF capacitance load, ESR of 20-120 ohms and 100 ppm frequency tolerance) connected externally between the XTAL1 and XTAL2 pins (see Figure 4), with an external 500 k to 1 M resistor across it. Alternatively, an external clock can be connected to the XTAL1 pin to clock the internal baud rate generator for standard or custom rates. Typical oscillator connections are shown in Figure 4. For further reading on oscillator circuit please see application note DAN108 on EXAR's web site. 9 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.9 Programmable Baud Rate Generator ac REV. 1.0.0 A single baud rate generator is provided for the transmitter and receiver, allowing independent TX/RX channel control. The programmable Baud Rate Generator is capable of operating with a crystal frequency of up to 24 MHz. However, with an external clock input on XTAL1 pin and a 2K ohms pull-up resistor on XTAL2 pin (as shown in Figure 5) it can extend its operation up to 64 MHz (4Mbps serial data rate) at room temperature and 5.0V. FIGURE 5. EXTERNAL CLOCK CONNECTION FOR EXTENDED DATA RATE External Clock vcc gnd XTAL1 VCC R1 2K XTAL2 To obtain maximum data rate, it is necessary to use full rail swing on the clock input. See external clock operating frequency over power supply voltage chart in Figure 6. FIGURE 6. OPERATING FREQUENCY CHART. REQUIRES A 2K OHMS PULL-UP RESISTOR ON XTAL2 PIN TO INCREASE OPERATING SPEED Operating frequency for XR16L2550 with external clock and a 2K ohms pull-up resistor on XTAL2 pin. XTAL1 External Clock Frequency in MHz. 80 70 60 50 40 30 3.0 3.5 4.0 -40oC 25oC 85oC 4.5 5.0 5.5 Suppy Voltage 10 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO The L2550 divides the basic external clock by 16. The basic 16X clock provides table rates to support standard and custom applications using the same system design. The Baud Rate Generator divides the input 16X clock by any divisor from 1 to 216 -1. The rate table is configured via the DLL and DLM internal register functions. Customized Baud Rates can be achieved by selecting the proper divisor values for the MSB and LSB sections of baud rate generator. Table 5 shows the standard data rates available with a 14.7456 MHz crystal or external clock at 16X sampling rate. When using a non-standard frequency crystal or external clock, the divisor value can be calculated for DLL/DLM with the following equation. divisor (decimal) = (XTAL1 clock frequency) / (serial data rate x 16) TABLE 5: TYPICAL DATA RATES WITH A 14.7456 MHZ CRYSTAL OR EXTERNAL CLOCK OUTPUT Data Rate MCR Bit-7=0 400 2400 4800 9600 19.2k 38.4k 76.8k 153.6k 230.4k 460.8k 921.6k DIVISOR FOR 16x Clock (Decimal) 2304 384 192 96 48 24 12 6 4 2 1 DIVISOR FOR 16x Clock (HEX) 900 180 C0 60 30 18 0C 06 04 02 01 DLM PROGRAM VALUE (HEX) 09 01 00 00 00 00 00 00 00 00 00 DLL PROGRAM VALUE (HEX) 00 80 C0 60 30 18 0C 06 04 02 01 DATA RATE ERROR (%) 0 0 0 0 0 0 0 0 0 0 0 2.10 Transmitter The transmitter section comprises of an 8-bit Transmit Shift Register (TSR) and 16 bytes of FIFO which includes a byte-wide Transmit Holding Register (THR). TSR shifts out every data bit with the 16X internal clock. A bit time is 16 clock periods. The transmitter sends the start-bit followed by the number of data bits, inserts the proper parity-bit if enabled, and adds the stop-bit(s). The status of the FIFO and TSR are reported in the Line Status Register (LSR bit-5 and bit-6). 2.10.1 Transmit Holding Register (THR) - Write Only The transmit holding register is an 8-bit register providing a data interface to the host processor. The host writes transmit data byte to the THR to be converted into a serial data stream including start-bit, data bits, parity-bit and stop-bit(s). The least-significant-bit (Bit-0) becomes first data bit to go out. The THR is the input register to the transmit FIFO of 16 bytes when FIFO operation is enabled by FCR bit-0. Every time a write operation is made to the THR, the FIFO data pointer is automatically bumped to the next sequential data location. 2.10.2 Transmitter Operation in non-FIFO Mode The host loads transmit data to THR one character at a time. The THR empty flag (LSR bit-5) is set when the data byte is transferred to TSR. THR flag can generate a transmit empty interrupt (ISR bit-1) when it is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when TSR becomes completely empty. 11 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO FIGURE 7. TRANSMITTER OPERATION IN NON-FIFO MODE ac REV. 1.0.0 Data Byte Transmit Holding Register (THR) THR Interrupt (ISR bit-1) Enabled by IER bit-1 16X Clock Transmit Shift Register (TSR) M S B L S B TXNOFIFO1 2.10.3 Transmitter Operation in FIFO Mode The host may fill the transmit FIFO with up to 16 bytes of transmit data. The THR empty flag (LSR bit-5) is set whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the transmit empty interrupt is enabled by IER bit-1. The TSR flag (LSR bit-6) is set when the FIFO and the TSR become empty. FIGURE 8. TRANSMITTER OPERATION IN FIFO AND FLOW CONTROL MODE Transmit Data Byte Transmit FIFO THR Interrupt (ISR bit-1) falls below the programmed Trigger Level and then when becom es empty. FIFO is Enabled by FCR bit-0=1 Auto CTS Flow Control (CTS# pin) Flow Control Characters (Xoff1/2 and Xon1/2 Reg. Auto Software Flow Control 16X Clock Transmit Data Shift Register (TSR) T XF IF O 1 2.11 Receiver The receiver section contains an 8-bit Receive Shift Register (RSR) and 16 bytes of FIFO which includes a byte-wide Receive Holding Register (RHR). The RSR uses the 16X for timing. It verifies and validates every bit on the incoming character in the middle of each data bit. On the falling edge of a start or false start bit, an internal receiver counter starts counting at the 16X. After 8 clocks the start bit period should be at the center of the start bit. At this time the start bit is sampled and if it is still a logic 0 it is validated. Evaluating the start bit in this manner prevents the receiver from assembling a false character. The rest of the data bits and stop bits are sampled and validated in this same manner to prevent false framing. If there were any error(s), they are reported in the LSR register bits 2-4. Upon unloading the receive data byte from RHR, the receive FIFO pointer is bumped and the error tags are immediately updated to reflect the status of the data byte in RHR register. RHR can generate a receive data ready interrupt upon receiving a character or delay until it reaches the FIFO trigger level. Furthermore, data delivery to the host is guaranteed by a receive data ready time-out interrupt 12 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO when data is not received for 4 word lengths as defined by LCR[1:0] plus 12 bits time. This is equivalent to 3.74.6 character times. The RHR interrupt is enabled by IER bit-0. 2.11.1 Receive Holding Register (RHR) - Read-Only The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift Register. It provides the receive data interface to the host processor. The RHR register is part of the receive FIFO of 16 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data byte are immediately updated in the LSR bits 2-4. FIGURE 9. RECEIVER OPERATION IN NON-FIFO MODE 16X Clock Receive Data Shift Register (RSR) Data Bit Validation Receive Data Characters Receive Data Byte and Errors Error Tags in LSR bits 4:2 Receive Data Holding Register (RHR) RHR Interrupt (ISR bit-2) RXFIFO1 FIGURE 10. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE 16X Clock Receive Data Shift Register (RSR) Data Bit Validation Receive Data Characters 16 bytes by 11-bit wide FIFO Error Tags (16-sets) Example : - RX FIFO trigger level selected at 8 bytes Data falls to 4 Receive Data FIFO RTS# re-asserts when data falls below the flow control trigger level to restart remote transmitter. Enable by EFR bit-6=1, MCR bit-2. RHR Interrupt (ISR bit-2) programmed for desired FIFO trigger level. FIFO is Enabled by FCR bit-0=1 RTS# de-asserts when data fills above the flow control trigger level to suspend remote transmitter. Enable by EFR bit-6=1, MCR bit-2. FIFO Trigger=8 Data fills to 14 Error Tags in LSR bits 4:2 Receive Data Byte and Errors Receive Data RXFIFO1 13 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.12 Auto RTS (Hardware) Flow Control ac REV. 1.0.0 Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS# output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control features is enabled to fit specific application requirement (see Figure 11): - Enable auto RTS flow control using EFR bit-6. - The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled). - Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1. 2.13 Auto CTS Flow Control Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific application requirement (see Figure 11): - Enable auto CTS flow control using EFR bit-7. - Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the CTS# pin is de-asserted (logic 1): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is re-asserted (logic 0), indicating more data may be sent. 14 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO FIGURE 11. AUTO RTS AND CTS FLOW CONTROL OPERATION Local UART UARTA Receiver FIFO Trigger Reached Auto RTS Trigger Level Transmitter Auto CTS Monitor RXA TXB Remote UART UARTB Transmitter Auto CTS Monitor Receiver FIFO Trigger Reached Auto RTS Trigger Level RTSA# TXA CTSB# RXB CTSA# Assert RTS# to Begin Transmission 1 ON 2 7 ON 3 8 OFF RTSB# RTSA# CTSB# TXB OFF 10 ON 11 ON Data Starts 4 RXA FIFO INTA (RXA FIFO Interrupt) Receive Data RX FIFO Trigger Level 5 6 Suspend Restart 9 RTS High Threshold RTS Low Threshold 12 RX FIFO Trigger Level RTSCTS1 The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO (4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and continues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows (7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its transmit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9), UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB with RTSB# and CTSA# controlling the data flow. 15 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.14 Auto Xon/Xoff (Software) Flow Control ac REV. 1.0.0 When software flow control is enabled (See Table 12), the L2550 compares one or two sequential receive data characters with the programmed Xon or Xoff-1,2 character value(s). If receive character(s) (RX) match the programmed values, the L2550 will halt transmission (TX) as soon as the current character has completed transmission. When a match occurs, the Xoff (if enabled via IER bit-5) flag will be set and the interrupt output pin will be activated. Following a suspension due to a match of the Xoff character, the L2550 will monitor the receive data stream for a match to the Xon-1,2 character. If a match is found, the L2550 will resume operation and clear the flags (ISR bit-4). Reset initially sets the contents of the Xon/Xoff 8-bit flow control registers to a logic 0. Following reset the user can write any Xon/Xoff value desired for software flow control. Different conditions can be set to detect Xon/ Xoff characters (See Table 12) and suspend/resume transmissions. When double 8-bit Xon/Xoff characters are selected, the L2550 compares two consecutive receive characters with two software flow control 8-bit values (Xon1, Xon2, Xoff1, Xoff2) and controls TX transmissions accordingly. Under the above described flow control mechanisms, flow control characters are not placed (stacked) in the user accessible RX data buffer or FIFO. In the event that the receive buffer is overfilling and flow control needs to be executed, the L2550 automatically sends an Xoff message (when enabled) via the serial TX output to the remote modem. The L2550 sends the Xoff-1,2 characters two-character-times (= time taken to send two characters at the programmed baud rate) after the receive FIFO crosses the programmed trigger level. To clear this condition, the L2550 will transmit the programmed Xon-1,2 characters as soon as receive FIFO is less than one trigger level below the programmed trigger level. See Table 6 below. TABLE 6: AUTO XON/XOFF (SOFTWARE) FLOW CONTROL RX TRIGGER LEVEL 1 4 8 14 INT PIN ACTIVATION 1 4 8 14 XOFF CHARACTER(S) SENT (CHARACTERS IN RX FIFO) 1* 4* 8* 14* XON CHARACTER(S) SENT (CHARACTERS IN RX FIFO) 0 1 4 8 * After the trigger level is reached, an xoff character is sent after a short span of time (= time required to send 2 characters); for example, after 2.083ms has elapsed for 9600 baud and 8-bit word length, no parity and 1 stop bit setting. 2.15 Special Character Detect A special character detect feature is provided to detect an 8-bit character when bit-5 is set in the Enhanced Feature Register (EFR). When this character (Xoff2) is detected, it will be placed in the FIFO along with normal incoming RX data. The L2550 compares each incoming receive character with Xoff-2 data. If a match exists, the received data will be transferred to FIFO and ISR bit-4 will be set to indicate detection of special character. Although the Internal Register Table shows Xon, Xoff Registers with eight bits of character information, the actual number of bits is dependent on the programmed word length. Line Control Register (LCR) bits 0-1 defines the number of character bits, i.e., either 5 bits, 6 bits, 7 bits, or 8 bits. The word length selected by LCR bits 0-1 also determines the number of bits that will be used for the special character comparison. Bit-0 in the Xon, Xoff Registers corresponds with the LSB bit for the receive character. 16 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.16 Infrared Mode The L2550 UART includes the infrared encoder and decoder compatible to the IrDA (Infrared Data Association) version 1.0. The IrDA 1.0 standard that stipulates the infrared encoder sends out a 3/16 of a bit wide HIGHpulse for each "0" bit in the transmit data stream. This signal encoding reduces the on-time of the infrared LED, hence reduces the power consumption. See Figure 12 below. The infrared encoder and decoder are enabled by setting MCR register bit-6 to a `1'. When the infrared feature is enabled, the transmit data output, TX, idles at logic zero level. Likewise, the RX input assumes an idle level of logic zero from a reset and power up, see Figure 12. Typically, the wireless infrared decoder receives the input pulse from the infrared sensing diode on the RX pin. Each time it senses a light pulse, it returns a logic 1 to the data bit stream. FIGURE 12. INFRARED TRANSMIT DATA ENCODING AND RECEIVE DATA DECODING C haracter Start D ata B its 1 0 1 0 0 1 1 0 Stop 1 1/2 B it T im e 3/16 B it T im e IrE ncoder-1 T X D ata 0 T ransm it IR P ulse (T X P in) B it T im e Receive IR Pulse (RX pin) Bit Time 1/16 Clock Delay RX Data 0 Start 1 0 1 0 0 1 1 0 1 Stop IRdecoder-1 Data Bits Character 17 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.17 Sleep Mode with Auto Wake-Up ac REV. 1.0.0 The L2550 supports low voltage system designs, hence, a sleep mode is included to reduce its power consumption when the chip is not actively used. All of these conditions must be satisfied for the L2550 to enter sleep mode: s s s s s no interrupts pending for both channels of the L2550 (ISR bit-0 = 1) divisor is a non-zero value (ie. DLL = 0x1) sleep mode of both channels are enabled (IER bit-4 = 1) modem inputs are not toggling (MSR bits 0-3 = 0) RX input pins are idling at a logic 1 The L2550 stops its crystal oscillator to conserve power in the sleep mode. User can check the XTAL2 pin for no clock output as an indication that the device has entered the sleep mode. The L2550 resumes normal operation by any of the following: s s s a receive data start bit transition (logic 1 to 0) a data byte is loaded to the transmitter, THR or FIFO a change of logic state on any of the modem or general purpose serial inputs: CTS#, DSR#, CD#, RI# If the L2550 is awakened by any one of the above conditions, it will return to the sleep mode automatically after all interrupting conditions have been serviced and cleared. If the 2750 is awakened by the modem inputs, a read to the MSR is required to reset the modem inputs. In any case, the sleep mode will not be entered while an interrupt is pending from channel A or B. The L2550 will stay in the sleep mode of operation until it is disabled by setting IER bit-4 to a logic 0. If the address lines, data bus lines, IOW#, IOR#, CSA#, CSB#, and modem input lines remain steady when the L2550 is in sleep mode, the maximum current will be in the microamp range as specified in the DC Electrical Characteristics on page 35. If the input lines are floating or are toggling while the L2550 is in sleep mode, the current can be up to 100 times more. If any of those signals are toggling or floating, then an external buffer would be required to keep the address, data and control lines steady to achieve the low current. As an alternative, please refer to the XR16L2551 which is pin-to-pin and software compatible with the L2550 but with (some additional pins and) the PowerSave feature that eliminates any unnecessary external buffer. Important: owing to the starting up delay of the crystal oscillator after waking up from sleep mode, the first few receive characters may be lost. The number of characters lost during the restart also depends on your operating data rate. More characters are lost when operating at higher data rate. Also, it is important to keep RX A/B inputs idling at logic 1 or "marking" condition during sleep mode to avoid receiving a "break" condition upon the restart. This may occur when the external interface transceivers (RS-232, RS-485 or another type) are also put to sleep mode and cannot maintain the "marking" condition. To avoid this, the designer can use a 47k-100k ohm pull-up resistor on the RXA and RXB pins. 18 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 2.18 Internal Loopback The L2550 UART provides an internal loopback capability for system diagnostic purposes. The internal loopback mode is enabled by setting MCR register bit-4 to logic 1. All regular UART functions operate normally. Figure 13 shows how the modem port signals are re-configured. Transmit data from the transmit shift register output is internally routed to the receive shift register input allowing the system to receive the same data that it was sending. The TX pin is held at logic 1 or mark condition while RTS# and DTR# are de-asserted, and CTS#, DSR# CD# and RI# inputs are ignored. Caution: the RX input pins must be held to a logic 1 during loopback test else upon exiting the loopback test the UART may detect and report a false "break" signal. Also, Auto RTS/CTS is not supported during internal loopback. FIGURE 13. INTERNAL LOOP BACK IN CHANNEL A AND B VCC Transmit Shift Register (THR/FIFO) MCR bit-4=1 Internal Data Bus Lines and Control Signals Receive Shift Register (RHR/FIFO) VCC RTS# Modem / General Purpose Control Logic RTSA#/RTSB# TXA/TXB RXA/RXB CTS# VCC DTR# CTSA#/CTSB# DTRA#/DTRB# DSR# OP1# RI# VCC OP2# DSRA#/DSRB# RIA#/RIB# OP2A#/OP2B# CD# CDA#/CDB# 19 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 3.0 UART INTERNAL REGISTERS ac REV. 1.0.0 Each of the UART channel in the L2550 has its own set of configuration registers selected by address lines A0, A1 and A2 with CSA# or CSB# selecting the channel. The registers are 16C550 compatible. The complete register set is shown on Table 7 and Table 8....INTERNAL Register descriptions TABLE 7: UART CHANNEL A AND B UART INTERNAL REGISTERS A2,A1,A0 ADDRESSES REGISTER READ/WRITE COMMENTS 16C550 COMPATIBLE REGISTERS 0 00 RHR - Receive Holding Register THR - Transmit Holding Register DLL - Div Latch Low Byte DLM - Div Latch High Byte IER - Interrupt Enable Register ISR - Interrupt Status Register FCR - FIFO Control Register LCR - Line Control Register MCR - Modem Control Register LSR - Line Status Register Reserved MSR - Modem Status Register Reserved SPR - Scratch Pad Register ENHANCED REGISTERS 0 1 1 1 1 10 00 01 10 11 EFR - Enhanced Function Register Xon-1 - Xon Character 1 Xon-2 - Xon Character 2 Xoff-1 - Xoff Character 1 Xoff-2 - Xoff Character 2 Read/Write Read/Write Read/Write Read/Write Read/Write LCR = 0xBF Read-only Write-only Read/Write Read/Write Read/Write Read-only Write-only Read/Write Read/Write Read-only Write-only Read-only Write-only Read/Write LCR[7] = 0 LCR 0xBF LCR[7] = 0 0 0 0 0 00 01 01 10 LCR[7] = 1, LCR 0xBF 0 1 1 11 00 01 LCR 0xBF 1 10 1 11 TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1 ADDRESS A2-A0 REG NAME READ/ WRITE BIT-7 BIT-6 BIT-5 BIT-4 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT 16C550 Compatible Registers 000 000 001 RHR THR IER RD WR RD/WR Bit-7 Bit-7 0/ Bit-6 Bit-6 0/ Bit-5 Bit-5 0/ Xoff Int. Enable Bit-4 Bit-4 0/ Sleep Mode Enable Bit-3 Bit-3 Bit-2 Bit-2 Bit-1 Bit-1 Bit-0 Bit-0 LCR[7] = 0 CTS Int. RTS Int. Enable Enable Modem RX Line TX RX Stat. Stat. Empty Data Int Int. Int. Int. Enable Enable Enable Enable 20 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO TABLE 8: INTERNAL REGISTERS DESCRIPTION. SHADED BITS ARE ENABLED WHEN EFR BIT-4=1 ADDRESS A2-A0 010 REG NAME ISR READ/ WRITE RD BIT-7 BIT-6 BIT-5 0/ INT Source Bit-5 0 BIT-4 0/ INT Source Bit-4 0 BIT-3 BIT-2 BIT-1 BIT-0 COMMENT FIFOs FIFOs Enabled Enabled INT INT INT INT Source Source Source Source Bit-3 Bit-2 Bit-1 Bit-0 LCR 0xBF DMA Mode Enable Parity Enable TX FIFO Reset Stop Bits RX FIFO Reset FIFOs Enable 010 FCR WR RX FIFO RX FIFO Trigger Trigger Divisor Enable Set TX Break 011 LCR RD/WR Set Parity Even Parity Word Word Length Length Bit-1 Bit-0 100 MCR RD/WR 0/ BRG Prescaler Internal OP2#/ Rsvd RTS# DTR# Lopback INT (OP1#) Output Output IR Mode XonAny Enable Output Control Control ENable Enable THR & TSR Empty RI# Input Bit-6 THR Empty RX Break RX Framing Error Delta CD# Bit-3 RX Parity Error Delta RI# Bit-2 RX Overrun Error Delta DSR# Bit-1 RX Data Ready Delta CTS# Bit-0 0/ 0/ 101 LSR RD RX FIFO Global Error CD# Input Bit-7 LCR 0xBF 110 111 MSR SPR RD RD/WR DSR# Input Bit-5 CTS# Input Bit-4 Baud Rate Generator Divisor 000 001 DLL DLM RD/WR RD/WR Bit-7 Bit-7 Bit-6 Bit-6 Bit-5 Bit-5 Bit-4 Bit-4 Bit-3 Bit-3 Bit-2 Bit-2 Bit-1 Bit-1 Bit-0 Bit-0 LCR[7] = 1 LCR 0xBF Enhanced Registers 010 EFR RD/WR Auto CTS Enable Auto RTS Enable Special Char Select Enable IER [7:4], ISR [5:4], FCR[5:4], MCR[7:5] Software Flow Cntl Bit-3 Bit-3 Bit-3 Bit-3 Bit-3 Software Flow Cntl Bit-2 Bit-2 Bit-2 Bit-2 Bit-2 Software Flow Cntl Bit-1 Bit-1 Bit-1 Bit-1 Bit-1 Software Flow Cntl Bit-0 Bit-0 Bit-0 Bit-0 Bit-0 LCR=0XBF 100 101 110 111 XON1 RD/WR XON2 RD/WR XOFF1 RD/WR XOFF2 RD/WR Bit-7 Bit-7 Bit-7 Bit-7 Bit-6 Bit-6 Bit-6 Bit-6 Bit-5 Bit-5 Bit-5 Bit-5 Bit-4 Bit-4 Bit-4 Bit-4 3.1 3.2 3.3 Receive Holding Register (RHR) - Read- Only Transmit Holding Register (THR) - Write-Only Interrupt Enable Register (IER) - Read/Write See "Receiver" on page 12. See "Transmitter" on page 11. 21 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 The Interrupt Enable Register (IER) masks the interrupts from receive data ready, transmit empty, line status and modem status registers. These interrupts are reported in the Interrupt Status Register (ISR). 3.3.1 IER versus Receive FIFO Interrupt Mode Operation When the receive FIFO (FCR BIT-0 = 1) and receive interrupts (IER BIT-0 = 1) are enabled, the RHR interrupts (see ISR bits 2 and 3) status will reflect the following: A. The receive data available interrupts are issued to the host when the FIFO has reached the programmed trigger level. It will be cleared when the FIFO drops below the programmed trigger level. B. FIFO level will be reflected in the ISR register when the FIFO trigger level is reached. Both the ISR register status bit and the interrupt will be cleared when the FIFO drops below the trigger level. C. The receive data ready bit (LSR BIT-0) is set as soon as a character is transferred from the shift register to the receive FIFO. It is reset when the FIFO is empty. 3.3.2 IER versus Receive/Transmit FIFO Polled Mode Operation When FCR BIT-0 equals a logic 1 for FIFO enable; resetting IER bits 0-3 enables the XR16L2550 in the FIFO polled mode of operation. Since the receiver and transmitter have separate bits in the LSR either or both can be used in the polled mode by selecting respective transmit or receive control bit(s). A. LSR BIT-0 indicates there is data in RHR or RX FIFO. B. LSR BIT-1 indicates an overrun error has occurred and that data in the FIFO may not be valid. C. LSR BIT 2-4 provides the type of receive data errors encountered for the data byte in RHR, if any. D. LSR BIT-5 indicates Transmit FIFO is empty. E. LSR BIT-6 indicates when both the transmit FIFO and TSR are empty. F. LSR BIT-7 indicates a data error in at least one character in the RX FIFO. 22 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO IER[0]: RHR Interrupt Enable The receive data ready interrupt will be issued when RHR has a data character in the non-FIFO mode or when the receive FIFO has reached the programmed trigger level in the FIFO mode. * Logic 0 = Disable the receive data ready interrupt (default). * Logic 1 = Enable the receiver data ready interrupt. IER[1]: THR Interrupt Enable This bit enables the Transmit Ready interrupt which is issued whenever the Transmit FIFO becomes empty. If the Transmit FIFO is empty when this bit is enabled, an interrupt will be generated. * Logic 0 = Disable Transmit Ready interrupt (default). * Logic 1 = Enable Transmit Ready interrupt. IER[2]: Receive Line Status Interrupt Enable If any of the LSR register bits 1, 2, 3 or 4 is a logic 1, it will generate an interrupt to inform the host controller about the error status of the current data byte in FIFO. LSR bit-1 generates an interrupt immediately when the character has been received. LSR bits 2-4 generate an interrupt when the character with errors is read out of the FIFO. * Logic 0 = Disable the receiver line status interrupt (default). * Logic 1 = Enable the receiver line status interrupt. IER[3]: Modem Status Interrupt Enable * Logic 0 = Disable the modem status register interrupt (default). * Logic 1 = Enable the modem status register interrupt. IER[4]: Sleep Mode Enable (requires EFR bit-4 = 1) * Logic 0 = Disable Sleep Mode (default). * Logic 1 = Enable Sleep Mode. See Sleep Mode section for further details. IER[5]: Xoff Interrupt Enable (requires EFR bit-4=1) * Logic 0 = Disable the software flow control, receive Xoff interrupt. (default) * Logic 1 = Enable the software flow control, receive Xoff interrupt. See Software Flow Control section for details. IER[6]: RTS# Output Interrupt Enable (requires EFR bit-4=1) * Logic 0 = Disable the RTS# interrupt (default). * Logic 1 = Enable the RTS# interrupt. The UART issues an interrupt when the RTS# pin makes a transition from low to high. IER[7]: CTS# Input Interrupt Enable (requires EFR bit-4=1) * Logic 0 = Disable the CTS# interrupt (default). * Logic 1 = Enable the CTS# interrupt. The UART issues an interrupt when CTS# pin makes a transition from low to high. 3.4 Interrupt Status Register (ISR) - Read-Only The UART provides multiple levels of prioritized interrupts to minimize external software interaction. The Interrupt Status Register (ISR) provides the user with six interrupt status bits. Performing a read cycle on the ISR will give the user the current highest pending interrupt level to be serviced, others are queued up to be serviced next. No other interrupts are acknowledged until the pending interrupt is serviced. The Interrupt Source Table, Table 9, shows the data values (bit 0-5) for the interrupt priority levels and the interrupt sources associated with each of these interrupt levels. 23 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO 3.4.1 Interrupt Generation: ac REV. 1.0.0 * LSR is by any of the LSR bits 1, 2, 3 and 4. * RXRDY is by RX trigger level. * RXRDY Time-out is by a 4-char plus 12 bits delay timer. * TXRDY is by TX FIFO empty. * MSR is by any of the MSR bits 0, 1, 2 and 3. * Receive Xoff/Special character is by detection of a Xoff or Special character. * CTS# is when its transmitter toggles the input pin (from low to high) during auto CTS flow control enabled by EFR bit-7. * RTS# is when its receiver toggles the output pin (from low to high) during auto RTS flow control enabled by EFR bit-6. 3.4.2 Interrupt Clearing: * LSR interrupt is cleared by a read to the LSR register (but flags and tags not cleared until character(s) that generated the interrupt(s) has been emptied or cleared from FIFO). * RXRDY interrupt is cleared by reading data until FIFO falls below the trigger level. * RXRDY Time-out interrupt is cleared by reading RHR. * TXRDY interrupt is cleared by a read to the ISR register or writing to THR. * MSR interrupt is cleared by a read to the MSR register. * Xoff interrupt is cleared by a read to ISR or when Xon character(s) is received. * Special character interrupt is cleared by a read to ISR or after the next character is received. * RTS# and CTS# flow control interrupts are cleared by a read to the MSR register. ] TABLE 9: INTERRUPT SOURCE AND PRIORITY LEVEL PRIORITY LEVEL 1 2 3 4 5 6 7 BIT-5 0 0 0 0 0 0 1 0 ISR REGISTER STATUS BITS BIT-4 0 0 0 0 0 1 0 0 BIT-3 0 1 0 0 0 0 0 0 BIT-2 1 1 1 0 0 0 0 0 BIT-1 1 0 0 1 0 0 0 0 BIT-0 0 0 0 0 0 0 0 1 LSR (Receiver Line Status Register) RXRDY (Receive Data Time-out) RXRDY (Received Data Ready) TXRDY (Transmit Ready) MSR (Modem Status Register) RXRDY (Received Xoff or Special character) CTS#, RTS# change of state None (default) SOURCE OF INTERRUPT ISR[0]: Interrupt Status * Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt service routine. * Logic 1 = No interrupt pending (default condition). ISR[3:1]: Interrupt Status 24 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO These bits indicate the source for a pending interrupt at interrupt priority levels (See Interrupt Source Table 9). 25 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ISR[4]: Xoff or Special Character Interrupt Status ac REV. 1.0.0 This bit is enabled when EFR bit-4 is set to a logic 1. ISR bit-4 indicates that the receiver detected a data match of the Xoff character(s). If this is an Xoff interrupt, it can be cleared by a read to the ISR or when an Xon character is received. If it is a special character interrupt, it will automatically clear after the next character is received. ISR[5]: RTS#/CTS# Interrupt Status This bit is enabled when EFR bit-4 is set to a logic 1. ISR bit-5 indicates that the CTS# or RTS# has changed state from low to high. ISR[7:6]: FIFO Enable Status These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are enabled. 3.5 FIFO Control Register (FCR) - Write-Only This register is used to enable the FIFOs, clear the FIFOs, set the transmit/receive FIFO trigger levels, and select the DMA mode. The DMA, and FIFO modes are defined as follows: FCR[0]: TX and RX FIFO Enable * Logic 0 = Disable the transmit and receive FIFO (default). * Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are written or they will not be programmed. FCR[1]: RX FIFO Reset This bit is only active when FCR bit-0 is a `1'. * Logic 0 = No receive FIFO reset (default) * Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (the receive shift register is not cleared or altered). This bit will return to a logic 0 after resetting the FIFO. FCR[2]: TX FIFO Reset This bit is only active when FCR bit-0 is a `1'. * Logic 0 = No transmit FIFO reset (default). * Logic 1 = Reset the transmit FIFO pointers and FIFO level counter logic (the transmit shift register is not cleared or altered). This bit will return to a logic 0 after resetting the FIFO. FCR[3]: DMA Mode Select Controls the behavior of theTXRDY# and RXRDY# pins. See DMA operation section for details. * Logic 0 = Normal Operation (default). * Logic 1 = DMA Mode. FCR[5:4]: Reserved FCR[7:6]: Receive FIFO Trigger Select (logic 0 = default, RX trigger level =1) These 2 bits are used to set the trigger level for the receive FIFO. The UART will issue a receive interrupt when the number of the characters in the FIFO crosses the trigger level. Table 10 shows the complete selections. 26 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO TABLE 10: RECEIVE FIFO TRIGGER LEVEL SELECTION FCR BIT-7 0 0 1 1 FCR BIT-6 0 1 0 1 RECEIVE TRIGGER LEVEL 1 (default) 4 8 14 COMPATIBILITY 16C550, 16C2550, 16C2552, 16C554, 16C580 compatible. 3.6 Line Control Register (LCR) - Read/Write The Line Control Register is used to specify the asynchronous data communication format. The word or character length, the number of stop bits, and the parity are selected by writing the appropriate bits in this register. LCR[1:0]: TX and RX Word Length Select These two bits specify the word length to be transmitted or received. BIT-1 0 0 1 1 BIT-0 0 1 0 1 WORD LENGTH 5 (default) 6 7 8 LCR[2]: TX and RX Stop-bit Length Select The length of stop bit is specified by this bit in conjunction with the programmed word length. BIT-2 0 1 1 WORD LENGTH 5,6,7,8 5 6,7,8 STOP BIT LENGTH (BIT TIME(S)) 1 (default) 1-1/2 2 LCR[3]: TX and RX Parity Select Parity or no parity can be selected via this bit. The parity bit is a simple way used in communications for data integrity check. See Table 11 for parity selection summary below. * Logic 0 = No parity. * Logic 1 = A parity bit is generated during the transmission while the receiver checks for parity error of the data character received. LCR[4]: TX and RX Parity Select If the parity bit is enabled with LCR bit-3 set to a logic 1, LCR BIT-4 selects the even or odd parity format. * Logic 0 = ODD Parity is generated by forcing an odd number of logic 1's in the transmitted character. The receiver must be programmed to check the same format (default). * Logic 1 = EVEN Parity is generated by forcing an even number of logic 1's in the transmitted character. The receiver must be programmed to check the same format. 27 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO LCR[5]: TX and RX Parity Select If the parity bit is enabled, LCR BIT-5 selects the forced parity format. ac REV. 1.0.0 * LCR[5] = logic 0, parity is not forced (default). * LCR[5] = logic 1 and LCR[4] = logic 0, parity bit is forced to a logical 1 for the transmit and receive data. * LCR[5] = logic 1 and LCR[4] = logic 1, parity bit is forced to a logical 0 for the transmit and receive data. TABLE 11: PARITY SELECTION LCR BIT-5 LCR BIT-4 LCR BIT-3 X 0 0 1 1 X 0 1 0 1 0 1 1 1 1 PARITY SELECTION No parity Odd parity Even parity Force parity to mark, "1" Forced parity to space, "0" LCR[6]: Transmit Break Enable When enabled, the Break control bit causes a break condition to be transmitted (the TX output is forced to a "space', logic 0, state). This condition remains, until disabled by setting LCR bit-6 to a logic 0. * Logic 0 = No TX break condition (default). * Logic 1 = Forces the transmitter output (TX) to a "space", logic 0, for alerting the remote receiver of a line break condition. LCR[7]: Baud Rate Divisors (DLL/DLM) Enable * Logic 0 = Data registers are selected (default). * Logic 1 = Divisor latch registers are selected. 3.7 Modem Control Register (MCR) or General Purpose Outputs Control - Read/Write The MCR register is used for controlling the serial/modem interface signals or general purpose inputs/outputs. MCR[0]: DTR# Output The DTR# pin is a modem control output. If the modem interface is not used, this output may be used as a general purpose output. * Logic 0 = Force DTR# output to a logic 1 (default). * Logic 1 = Force DTR# output to a logic 0. MCR[1]: RTS# Output The RTS# pin is a modem control output. If the modem interface is not used, this output may be used as a general purpose output. * Logic 0 = Force RTS# output to a logic 1 (default). * Logic 1 = Force RTS# output to a logic 0. MCR[2]: Reserved OP1# is not available as an output pin on the L2550. But it is available for use during Internal Loopback Mode. In the Loopback Mode, this bit is used to write the state of the modem RI# interface signal. 28 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO MCR[3]: OP2# Output / INT Output Enable This bit enables and disables the operation of INT, interrupt output. If INT output is not used, OP2# can be used as a general purpose output. * Logic 0 = INT (A-B) outputs disabled (three state mode) and OP2# output set to a logic 1 (default). * Logic 1 = INT (A-B) outputs enabled (active mode) and OP2# output set to a logic 0. MCR[4]: Internal Loopback Enable * Logic 0 = Disable loopback mode (default). * Logic 1 = Enable local loopback mode, see loopback section and Figure 13. MCR[5]: Xon-Any Enable * Logic 0 = Disable Xon-Any function (for 16C550 compatibility, default). * Logic 1 = Enable Xon-Any function. In this mode, any RX character received will resume transmit operation. The RX character will be loaded into the RX FIFO , unless the RX character is an Xon or Xoff character and the L2552 is programmed to use the Xon/Xoff flow control. MCR[6]: Infrared Encoder/Decoder Enable * Logic 0 = Enable the standard modem receive and transmit input/output interface. (Default) * Logic 1 = Enable infrared IrDA receive and transmit inputs/outputs. The TX/RX output/input are routed to the infrared encoder/decoder. The data input and output levels conform to the IrDA infrared interface requirement. While in this mode, the infrared TX output will be a logic 0 during idle data conditions. MCR[7]: Clock Prescaler Select * Logic 0 = Divide by one. The input clock from the crystal or external clock is fed directly to the Programmable Baud Rate Generator without further modification, i.e., divide by one (default). * Logic 1 = Divide by four. The prescaler divides the input clock from the crystal or external clock by four and feeds it to the Programmable Baud Rate Generator, hence, data rates become one forth. 3.8 Line Status Register (LSR) - Read Only This register provides the status of data transfers between the UART and the host. LSR[0]: Receive Data Ready Indicator * Logic 0 = No data in receive holding register or FIFO (default). * Logic 1 = Data has been received and is saved in the receive holding register or FIFO. LSR[1]: Receiver Overrun Flag * Logic 0 = No overrun error (default). * Logic 1 = Overrun error. A data overrun error condition occurred in the receive shift register. This happens when additional data arrives while the FIFO is full. In this case the previous data in the receive shift register is overwritten. Note that under this condition the data byte in the receive shift register is not transferred into the FIFO, therefore the data in the FIFO is not corrupted by the error. An interrupt will be generated immediately if LSR interrupt is enabled (IER bit-2). LSR[2]: Receive Data Parity Error Flag * Logic 0 = No parity error (default). * Logic 1 = Parity error. The receive character in RHR does not have correct parity information and is suspect. This error is associated with the character available for reading in RHR. If the LSR interrupt is enabled (IER bit-2), an interrupt will be generated when the character is in the RHR. 29 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO LSR[3]: Receive Data Framing Error Flag ac REV. 1.0.0 * Logic 0 = No framing error (default). * Logic 1 = Framing error. The receive character did not have a valid stop bit(s). This error is associated with the character available for reading in RHR. If the LSR interrupt is enabled (IER bit-2), an interrupt will be generated when the character is in the RHR. LSR[4]: Receive Break Flag * Logic 0 = No break condition (default). * Logic 1 = The receiver received a break signal (RX was a logic 0 for at least one character frame time). In the FIFO mode, only one break character is loaded into the FIFO. The break indication remains until the RX input returns to the idle condition, "mark" or logic 1. If the LSR interrupt is enabled (IER bit-2), an interrupt will be generated when the character is in the RHR. LSR[5]: Transmit Holding Register Empty Flag This bit is the Transmit Holding Register Empty indicator. This bit indicates that the transmitter is ready to accept a new character for transmission. In addition, this bit causes the UART to issue an interrupt to the host when the THR interrupt enable is set. The THR bit is set to a logic 1 when the last data byte is transferred from the transmit holding register to the transmit shift register. The bit is reset to logic 0 concurrently with the data loading to the transmit holding register by the host. In the FIFO mode this bit is set when the transmit FIFO is empty, it is cleared when the transmit FIFO contains at least 1 byte. LSR[6]: THR and TSR Empty Flag This bit is set to a logic 1 whenever the transmitter goes idle. It is set to logic 0 whenever either the THR or TSR contains a data character. In the FIFO mode this bit is set to a logic 1 whenever the transmit FIFO and transmit shift register are both empty. LSR[7]: Receive FIFO Data Error Flag * Logic 0 = No FIFO error (default). * Logic 1 = A global indicator for the sum of all error bits in the RX FIFO. At least one parity error, framing error or break indication is in the FIFO data. This bit clears when there is no more error(s) in the FIFO. 3.9 Modem Status Register (MSR) - Read Only This register provides the current state of the modem interface signals, or other peripheral device that the UART is connected. Lower four bits of this register are used to indicate the changed information. These bits are set to a logic 1 whenever a signal from the modem changes state. These bits may be used as general purpose inputs/outputs when they are not used with modem signals. MSR[0]: Delta CTS# Input Flag * Logic 0 = No change on CTS# input (default). * Logic 1 = The CTS# input has changed state since the last time it was monitored. A modem status interrupt will be generated if MSR interrupt is enabled (IER bit-3). MSR[1]: Delta DSR# Input Flag * Logic 0 = No change on DSR# input (default). * Logic 1 = The DSR# input has changed state since the last time it was monitored. A modem status interrupt will be generated if MSR interrupt is enabled (IER bit-3). MSR[2]: Delta RI# Input Flag * Logic 0 = No change on RI# input (default). * Logic 1 = The RI# input has changed from a logic 0 to a logic 1, ending of the ringing signal. A modem status interrupt will be generated if MSR interrupt is enabled (IER bit-3). 30 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO MSR[3]: Delta CD# Input Flag * Logic 0 = No change on CD# input (default). * Logic 1 = Indicates that the CD# input has changed state since the last time it was monitored. A modem status interrupt will be generated if MSR interrupt is enabled (IER bit-3). MSR[4]: CTS Input Status Normally this bit is the compliment of the CTS# input. However in the loopback mode, this bit is equivalent to the RTS# bit in the MCR register. The CTS# input may be used as a general purpose input when the modem interface is not used. MSR[5]: DSR Input Status Normally this bit is the compliment of the DSR# input. In the loopback mode, this bit is equivalent to the DTR# bit in the MCR register. The DSR# input may be used as a general purpose input when the modem interface is not used. MSR[6]: RI Input Status Normally this bit is the compliment of the RI# input. In the loopback mode this bit is equivalent to bit-2 in the MCR register. The RI# input may be used as a general purpose input when the modem interface is not used. MSR[7]: CD Input Status Normally this bit is the compliment of the CD# input. In the loopback mode this bit is equivalent to bit-3 in the MCR register. The CD# input may be used as a general purpose input when the modem interface is not used. 3.10 Scratch Pad Register (SPR) - Read/Write This is a 8-bit general purpose register for the user to store temporary data. The content of this register is preserved during sleep mode but becomes 0xFF (default) after a reset or a power off-on cycle. 3.11 Baud Rate Generator Registers (DLL and DLM) - Read/Write The Baud Rate Generator (BRG) is a 16-bit counter that generates the data rate for the transmitter. The rate is programmed through registers DLL and DLM which are only accessible when LCR bit-7 is set to `1'. See "Programmable Baud Rate Generator" on page 10. for more details. 3.12 Enhanced Feature Register (EFR) Enhanced features are enabled or disabled using this register. Bit 0-3 provide single or dual consecutive character software flow control selection (see Table 12). When the Xon1 and Xon2 and Xoff1 and Xoff2 modes are selected, the double 8-bit words are concatenated into two sequential characters. Caution: note that whenever changing the TX or RX flow control bits, always reset all bits back to logic 0 (disable) before programming a new setting. 31 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO EFR[3:0]: Software Flow Control Select ac REV. 1.0.0 Single character and dual sequential characters software flow control is supported. Combinations of software flow control can be selected by programming these bits. TABLE 12: SOFTWARE FLOW CONTROL FUNCTIONS EFR BIT-3 CONT-3 0 0 1 0 1 X X X 1 EFR BIT-2 CONT-2 0 0 0 1 1 X X X 0 EFR BIT-1 CONT-1 0 X X X X 0 1 0 1 EFR BIT-0 CONT-0 0 X X X X 0 0 1 1 TRANSMIT AND RECEIVE SOFTWARE FLOW CONTROL No TX and RX flow control (default and reset) No transmit flow control Transmit Xon1, Xoff1 Transmit Xon2, Xoff2 Transmit Xon1 and Xon2, Xoff1 and Xoff2 No receive flow control Receiver compares Xon1, Xoff1 Receiver compares Xon2, Xoff2 Transmit Xon1, Xoff1 Receiver compares Xon1 or Xon2, Xoff1 or Xoff2 Transmit Xon2, Xoff2 Receiver compares Xon1 or Xon2, Xoff1 or Xoff2 Transmit Xon1 and Xon2, Xoff1 and Xoff2, Receiver compares Xon1 and Xon2, Xoff1 and Xoff2 No transmit flow control, Receiver compares Xon1 and Xon2, Xoff1 and Xoff2 0 1 1 1 1 1 1 1 0 0 1 1 EFR[4]: Enhanced Function Bits Enable Enhanced function control bit. This bit enables IER bits 4-7, ISR bits 4-5, and MCR bits 5-7 to be modified. After modifying any enhanced bits, EFR bit-4 can be set to a logic 0 to latch the new values. This feature prevents legacy software from altering or overwriting the enhanced functions once set. Normally, it is recommended to leave it enabled, logic 1. * Logic 0 = modification disable/latch enhanced features. IER bits 4-7, ISR bits 4-5, and MCR bits 5-7 are saved to retain the user settings. After a reset, the IER bits 4-7, ISR bits 4-5, and MCR bits 5-7are set to a logic 0 to be compatible with ST16C550 mode (default). * Logic 1 = Enables the above-mentioned register bits to be modified by the user. EFR[5]: Special Character Detect Enable * Logic 0 = Special Character Detect Disabled (default). * Logic 1 = Special Character Detect Enabled. The UART compares each incoming receive character with data in Xoff-2 register. If a match exists, the receive data will be transferred to FIFO and ISR bit-4 will be set to indicate detection of the special character. Bit-0 corresponds with the LSB bit of the receive character. If flow control is set for comparing Xon1, Xoff1 (EFR [1:0]= `10') then flow control and special character work normally. However, if flow control is set for comparing Xon2, Xoff2 (EFR[1:0]= `01') then flow control works normally, but Xoff2 will not go to the FIFO, and will generate an Xoff interrupt and a special character interrupt, if enabled via IER bit-5. Special character interrupts are cleared automatically after the next received character. EFR[6]: Auto RTS Flow Control Enable 32 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO RTS# output may be used for hardware flow control by setting EFR bit-6 to logic 1. When Auto RTS is selected, an interrupt will be generated when the receive FIFO is filled to the programmed trigger level and RTS deasserts to a logic 1 at the next upper trigger level. RTS# will return to a logic 0 when FIFO data falls below the next lower trigger level. The RTS# output must be asserted (logic 0) before the auto RTS can take effect. RTS# pin will function as a general purpose output when hardware flow control is disabled. * Logic 0 = Automatic RTS flow control is disabled (default). * Logic 1 = Enable Automatic RTS flow control. EFR[7]: Auto CTS Flow Control Enable Automatic CTS Flow Control. * Logic 0 = Automatic CTS flow control is disabled (default). * Logic 1 = Enable Automatic CTS flow control. Data transmission stops when CTS# input de-asserts to logic 1. Data transmission resumes when CTS# returns to a logic 0. 3.13 Software Flow Control Registers (XOFF1, XOFF2, XON1, XON2) - Read/Write These registers are used as the programmable software flow control characters XOFF1, XOFF2, XON1, and XON2. For more details, see Table 6. 33 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO TABLE 13: UART RESET CONDITIONS FOR CHANNEL A AND B REGISTERS DLM DLL RHR THR IER FCR ISR LCR MCR LSR MSR RESET STATE Bits 7-0 = 0xXX Bits 7-0 = 0xXX Bits 7-0 = 0xXX Bits 7-0 = 0xXX Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x01 Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x60 Bits 3-0 = Logic 0 Bits 7-4 = Logic levels of the inputs inverted Bits 7-0 = 0xFF Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x00 Bits 7-0 = 0x00 RESET STATE Logic 1 Logic 1 Logic 1 Logic 1 Logic 1 Logic 0 Three-State Condition ac REV. 1.0.0 SPR EFR XON1 XON2 XOFF1 XOFF2 I/O SIGNALS TX OP2# RTS# DTR# RXRDY# TXRDY# INT 34 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ABSOLUTE MAXIMUM RATINGS Power Supply Range Voltage at Any Pin Operating Temperature Storage Temperature Package Dissipation 7 Volts GND-0.3 V to VCC+0.3 V -40o to +85oC -65o to +150oC 500 mW TYPICAL PACKAGE THERMAL RESISTANCE DATA (MARGIN OF ERROR: 15%) Thermal Resistance (48-TQFP) Thermal Resistance (44-PLCC) Thermal Resistance (32-QFN) theta-ja =59oC/W, theta-jc = 16oC/W theta-ja = 50oC/W, theta-jc = 21oC/W theta-ja = oC/W, theta-jc = oC/W ELECTRICAL CHARACTERISTICS DC ELECTRICAL CHARACTERISTICS UNLESS OTHERWISE NOTED: TA=-40O TO +85OC, VCC IS 2.25 TO 5.5V SYMBOL VILCK VIHCK VIL VIH VOL PARAMETER Clock Input Low Level Clock Input High Level Input Low Voltage Input High Voltage Output Low Voltage 0.4 0.4 VOH Output High Voltage 2.0 1.8 IIL IIH CIN ICC ISLEEP Input Low Leakage Current Input High Leakage Current Input Pin Capacitance Power Supply Current Sleep Current 10 10 5 1 6 10 10 5 1.3 15 10 10 5 3 30 2.4 2.5V LIMITS MIN MAX -0.3 2.0 -0.3 2.0 0.2 5.5 0.6 5.5 3.3V LIMITS MIN MAX -0.3 2.4 -0.3 2.0 0.6 5.5 0.8 5.5 5.0V LIMITS MIN MAX -0.5 3.0 -0.5 2.2 0.6 5.5 0.8 5.5 0.4 UNITS V V V V V V V V V V uA uA pF mA uA See Test 1 IOL = 6 mA IOL = 4 mA IOL = 2 mA IOH = -6 mA IOH = -1 mA IOH = -400 uA CONDITIONS Test 1: The following inputs must remain steady at VCC or GND state to minimize Sleep current: A0-A2, D0D7, IOR#, IOW#, CSA#, CSB#, and all modem inputs. Also, RXA and RXB inputs must idle at logic 1 state while asleep. Floating inputs will result in sleep currents in the mA range. For PowerSave feature that isolates address, data and control signals, please see the XR16L2551 datasheet. 35 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 AC ELECTRICAL CHARACTERISTICS UNLESS OTHERWISE NOTED: TA=-40O TO +85OC, VCC IS 2.25V TO 5.5V, 70 PF LOAD WHERE APPLICABLE SYMBOL PARAMETER LIMITS 2.5 MIN MAX 16 31 16 10 10 150 150 150 125 0 150 150 25 15 150 150 150 1 150 150 8 24 150 1 150 150 8 40 40 8 45 0 75 75 20 10 75 75 75 1 75 75 24 75 1 75 75 8 40 8 10 10 75 75 75 80 30 0 50 50 15 10 50 50 50 1 50 50 24 50 1 50 50 8 17 30 10 10 50 50 50 50 30 LIMITS 3.3 MIN MAX 20 10 50 LIMITS 5.0 MIN MAX 24 MHz ns MHz ns ns ns ns ns ns ns ns ns ns ns ns ns ns Bclk ns ns Bclk ns Bclk ns ns Bclk ns UNIT CLK OSC TAS TAH TCS TRD TDY TRDV TDD TWR TDY TDS TDH TWDO TMOD TRSI TSSI TRRI TSI TINT TWRI TSSR TRR TWT TSRT TRST Crystal Frequency External Clock Low/High Time External Clock Frequency Address Setup Time Address Hold Time Chip Select Width IOR# Strobe Width Read Cycle Delay Data Access Time Data Disable Time IOW# Strobe Width Write Cycle Delay Data Setup Time Data Hold Time Delay From IOW# To Output Delay To Set Interrupt From MODEM Input Delay To Reset Interrupt From IOR# Delay From Stop To Set Interrupt Delay From IOR# To Reset Interrupt Delay From Stop To Interrupt Delay From Initial INT Reset To Transmit Start Delay From IOW# To Reset Interrupt Delay From Stop To Set RXRDY# Delay From IOR# To Reset RXRDY# Delay From IOW# To Set TXRDY# Delay From Center of Start To Reset TXRDY# Reset Pulse Width 36 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO AC ELECTRICAL CHARACTERISTICS UNLESS OTHERWISE NOTED: TA=-40O TO +85OC, VCC IS 2.25V TO 5.5V, 70 PF LOAD WHERE APPLICABLE SYMBOL PARAMETER LIMITS 2.5 MIN MAX 1 216-1 LIMITS 3.3 MIN MAX 1 216-1 LIMITS 5.0 MIN 1 MAX 216-1 Hz UNIT N Bclk Baud Rate Divisor Baud Clock 16X of data rate FIGURE 14. CLOCK TIMING CLK CLK EXTERNAL CLOCK OSC FIGURE 15. MODEM INPUT/OUTPUT TIMING FOR CHANNELS A & B IOW # Active T W DO RTS# DTR# Change of state Change of state CD# CTS# DSR# T MOD INT Change of state Change of state T MOD Active T RSI Active Active IOR# Active Active Active T MOD RI# Change of state 37 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO FIGURE 16. DATA BUS READ TIMING ac REV. 1.0.0 A0-A2 TAS Valid Address TAS Valid Address TCS CSA#/ CSB# TAH TCS TAH TDY TRD IOR# TRD TRDV D0-D7 Valid Data TDD TRDV Valid Data TDD RDTm FIGURE 17. DATA BUS WRITE TIMING A0-A2 TAS Valid Address TAS Valid Address TCS CSA#/ CSB# TAH TCS TAH TDY TWR IOW# TWR TDS D0-D7 Valid Data TDH TDS Valid Data TDH 16Write 38 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO FIGURE 18. RECEIVE READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B RX Start Bit Stop Bit TSSR 1 Byte in RHR TSSR D0:D7 D0:D7 TSSR 1 Byte in RHR TSSR D0:D7 TSSR 1 Byte in RHR TSSR INT RXRDY# Active Data Ready TRR Active Data Ready TRR Active Data Ready TRR IOR# (Reading data out of RHR) RXNFM FIGURE 19. TRANSMIT READY & INTERRUPT TIMING [NON-FIFO MODE] FOR CHANNELS A & B TX (Unloading) IER[1] enabled Start Bit Stop Bit D0:D7 D0:D7 D0:D7 ISR is read ISR is read ISR is read INT* TWRI TSRT TWRI TSRT TWRI TSRT TXRDY# TWT TWT TWT IOW# (Loading data into THR) *INT is cleared when the ISR is read or when data is loaded into the THR. TXNonFIFO 39 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 FIGURE 20. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA DISABLED] FOR CHANNELS A & B Start Bit RX S D0:D7 Stop Bit S D0:D7 T D0:D7 TSSI S D0:D7 T S D0:D7 T S D0:D7 T S D0:D7 T RX FIFO drops below RX Trigger Level INT TSSR RXRDY# First Byte is Received in RX FIFO IOR# (Reading data out of RX FIFO) RX FIFO fills up to RX Trigger Level or RX Data Timeout FIFO Empties TRRI TRR RXINTDMA# FIGURE 21. RECEIVE READY & INTERRUPT TIMING [FIFO MODE, DMA ENABLED] FOR CHANNELS A & B Start Bit Stop Bit RX S D0:D7 S D0:D7 T D0:D7 TSSI S D0:D7 T S D0:D7 T S D0:D7 T S D0:D7 T RX FIFO drops below RX Trigger Level INT RX FIFO fills up to RX Trigger Level or RX Data Timeout RXRDY# TSSR FIFO Empties TRRI TRR IOR# (Reading data out of RX FIFO) RXFIFODMA 40 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO FIGURE 22. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE DISABLED] FOR CHANNELS A & B Start Bit Stop Bit Last Data Byte Transmitted S D0:D7 T S D0:D7 T T S D0:D7 T S D0:D7 T S D0:D7 T TSRT TX FIFO no longer empty TX FIFO Empty TX (Unloading) IER[1] enabled S D0:D7 T ISR is read INT* TWRI Data in TX FIFO TSI TX FIFO Empty TXRDY# TWT IOW# (Loading data into FIFO) *INT is cleared when the ISR is read or when there is at least one character in the FIFO. TXDMA# FIGURE 23. TRANSMIT READY & INTERRUPT TIMING [FIFO MODE, DMA MODE ENABLED] FOR CHANNELS A & B Start Bit Stop Bit TX FIFO Empty Last Data Byte Transmitted S D0:D7 T S D0:D7 T T S D0:D7 T S D0:D7 T S D0:D7 T TX (Unloading) IER[1] enabled S D0:D7 T ISR is read TX FIFO no longer empty TSRT TSI INT* TWRI TX FIFO Empty TXRDY# TX FIFO Full At least 1 empty location in FIFO TWT IOW# (Loading data into FIFO) *INT is cleared when the ISR is read or when there is at least one character in the FIFO. TXDMA 41 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 PACKAGE DIMENSIONS (48 PIN TQFP - 7 X 7 X 1 mm) D D1 36 25 37 24 D1 D 48 13 1 B A2 e 1 2 C A Seating Plane A1 L Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A2 B C D D1 e L MIN 0.039 0.002 0.037 0.007 0.004 0.346 0.272 MAX 0.047 0.006 0.041 0.011 0.008 0.362 0.280 MILLIMETERS MIN 1.00 0.05 0.95 0.17 0.09 8.80 6.90 MAX 1.20 0.15 1.05 0.27 0.20 9.20 7.10 0.020 BSC 0.018 0 0.030 7 0.50 BSC 0.45 0 0.75 7 42 ac REV. 1.0.0 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO PACKAGE DIMENSIONS (44 PIN PLCC) 4 4 L E A D P L A S T IC L E A D E D C H IP C A R R IE R (P L C C ) R e v. 1 .00 D D1 4 5 x H 2 44 4 5 x H 1 C S e a tin g P la n e A2 2 1 B1 D D1 D3 B D2 e R D3 A1 A Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A2 B B1 C D D1 D2 D3 e H1 H2 R MIN 0.165 0.090 0.020 0.013 0.026 0.008 0.685 0.650 0.590 MAX 0.180 0.120 --0.021 0.032 0.013 0.695 0.656 0.630 MILLIMETERS MIN 4.19 2.29 0.51 0.33 0.66 0.19 17.40 16.51 14.99 MAX 4.57 3.05 --0.53 0.81 0.32 17.65 16.66 16.00 0.500 typ. 0.050 BSC 0.042 0.042 0.025 0.056 0.048 0.045 12.70 typ. 1.27 BSC 1.07 1.07 0.64 1.42 1.22 1.14 43 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 PACKAGE DIMENSIONS (32 PIN QFN - 5 X 5 X 0.9 mm) D D2 D D2 L e b A1 A3 A Steating Plane Note: The control dimension is the millimeter column INCHES SYMBOL A A1 A3 D D2 b e L MIN 0.031 0.000 0.006 0.193 0.138 0.007 MAX 0.039 0.002 0.010 0.201 0.150 0.012 MILLIMETERS MIN 0.80 0.00 0.15 4.90 3.50 0.18 MAX 1.00 0.05 0.25 5.10 3.80 0.30 0.0197 BSC 0.014 0.018 0.050 BSC 0.35 0.45 44 XR16L2550 LOW VOLTAGE DUART WITH 16-BYTE FIFO ac REV. 1.0.0 REVISION HISTORY Date Revision Preliminary Datasheet. Description November 2002 P1.0.0 March 2003 May 2003 June 2003 July 2003 P1.0.1 P1.0.2 P1.0.3 P1.0.4 Updated AC Electrical Characteristics. Updated register set with enhanced features. Added patent number to first page. Added 32 pin QFN package dimensions. Added Device Status to Ordering Information. Updated AC Electrical Characteristics. Final Production Release. Updated 5V tolerance information. September 2003 1.0.0 NOTICE EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Copyright 2003 EXAR Corporation Datasheet September 2003. Send your UART technical inquiry with technical details to hotline: uarttechsupport@exar.com. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. 45 |
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