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2.3 SCSI Bus Technology

2.3.2 Data Transfer Options

The SCSI protocol is designed to provide an efficient peer-to-peer I/O bus with up to 8, 16, or 32 devices depending on the data path widths implemented, including one or more hosts. Data may be transferred asynchronously at rates that depend primarily on device implementation and cable length. Synchronous data transfers are supported at rates up to 10 megatransfers per second. Three data path widths are allowed, 8-bit, 16-bit, and 32-bit. The corresponding maximum transfer rates are 10, 20, and 40 megabytes per second.

Data transfers are divided into three speed classes: asynchronous, slow, and fast. A transfer period specifies the minimum time allowed between the leading edges of successive REQ pulses and of successive ACK pulses while using synchronous data transfers.

  • Fast data transfers require a transfer period greater than 100 ns. and less than 200 ns. with a REQ/ACK offset greater than zero. If a fast data transfer is agreed upon, fast timing shall be observed even though the actual data transfer period is greater than or equal to 200 ns.
  • Slow data transfers require a transfer period greater than or equal to 200 ns. with a REQ/ACK offset greater than zero.
  • Asynchronous information transfers require a REQ/ACK offset of zero. The transfer period does not apply to these information transfers.
The BI0316 supports all three classes.


BI-0316 - Mass Storage Module - 6 DEC 1996 Copyright 1996 Brand Innovators B.V. [Next] [Previous] [Up] [Top] [Contents] [Back]