data sheet SYM53C770 single-chip high-performance ultra scsi (fast-20) i/o processor designed for use in multi-user systems including network file servers, multitasking mid-range computers, supercomputers, and minicomputers. ultra scsi (fast-20) technology doubles the i/o bandwidth up to 40 mb/s builds upon proven technology?a pin-for-pin replacement for the sym53c720 provides new features for enhanced performance and flexibility. the SYM53C770 includes all of the features of the sym53c720 with added support for ultra scsi (fast-20) transfers, enabling the chip to transfer scsi data at up to 20 mb/s on an 8-bit bus and up to 40 mb/s on a 16-bit bus. fast-20 is an extension of the scsi- 3 standard that expands the bandwidth of the scsi bus and allows faster synchronous scsi transfer rates. when enabled, fast-20 effectively doubles the synchronous transfer rates of fast scsi-2. the SYM53C770 allows easy firmware upgrades and is scripts? -compatible (the symbios? -developed scsi programming language) with the sym53c7xx and sym53c8xx families. the device provides full scsi-2 capabilities and features symbios tolerant? scsi driver and receiver technology for reliable operation in all cabling environments. performance enhancements of the SYM53C770 include an additional 4 kb of internal ram for scripts instruction storage, which reduces system bus bandwidth requirements, and allows tailored scsi sequences to be executed locally--saving the system bandwidth for other tasks. a 96-byte dma fifo provides more efficient throughput from/to the host to/from the scsi bus during high latency dma bus requests. other new features include: an increase in the maximum synchronous scsi offset from 8 to 16 levels--allowing better speed matching during fast-20 transfers a scsi clock doubler allows the use of a 40/50 mhz oscillator, which is doubled internally to provide the correct frequency for fast-20 transfer modes
expanded handshake-to-handshake and general purpose timers to include a scale factor to increase the length of time before these timers expire features and benefits performance performs scsi fast-20 data transfers up to: 40 mb/s synchronous (16-bit) 20 mb/s synchronous (8-bit) functions as full 32-bit dma bus master additional 4 kb scripts internal ram 96-byte dma fifo for improved throughput between the host and scsi bus scsi offset increased to 16 transfers 32 additional scratchpad registers for user-defined functions ease-of-use pin-for-pin replacement for sym53c720 minimal software and hardware modifications required for fast-20 support allows migration of existing sym53c7xx scripts handshake-to-handshake and general purpose timers include a scale factor to increase amount of time before timers expire flexibility internal scsi clock doubler allows use of a 40/50mhz oscillator with fast-20 transfer modes scsi selected as id register high-level programming interface (scsi scripts) allows tailored scsi sequences to be executed from main memory accommodates changes in the logical i/o interface definition symbios, scripts, and tolerant are trademarks of symbios inc.
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