Adaptec 1742A Standard Mode, Synchronous Data Transfer Negotiation, Tagged Queuing, Target

adaptec AHA-1740A/1742A/1744

Standard Mode

The operation mode that allows software written for the AHA- 1540/1640 family to be fully compatible with the AHA-1740A/ 1742A/1744. The limitation is that you cannot select addresses beyond 16 MBytes or access several EISA registers.

Synchronous Data Transfer

A method of data transfer on the SCSI bus involving clocking data on to the bus with a fixed-length fixed-frequency strobe pulses. The acknowledgments may be delayed several clock peri- ods from the data requests. Synchronous data transfer can be used only for data transmission on the SCSI bus. It is prohibited for command, message, and status transmission.

Synchronous Data Transfer Negotiation

The message exchange between the initiator and the target that allows the negotiation of the data transfer frequency and delay between requests and acknowledgments required for synchronous data transfer. Once negotiated, synchronous data transfer pa- rameters remain unchanged until certain reinitialization activi- ties occur.

Tagged Queuing

A SCSI-2 feature that allows the SCSI device to return data in a different order than requested by the SCSI host adapter.

Target

A SCSI device that performs an operation requested by an initia- tor. The target may be a peripheral device performing a service for an initiator. The target may also be a host adapter performing a processor-type device service for an initiator.

Word

A 2-byte (16-bit) unit of data.

Zero Latency Reads

A Method of minimizing mechanical limitations of fixed disk by re- questing data in an unordered sequence. The data is reordered by the host adapter.

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