Avago Technologies LSI53C1020 - Manual (Page 44)

2-18 Functional Description
Version 2.4 Copyright © 2001–2004 by LSI Logic Corporation. All rights reserved.
2.4 Ultra320 SCSI Functional Description
The Ultra320 SCSI channel supports wide SCSI synchronous transfer
rates up to 320 Mbytes/s across an SE or LVD SCSI bus. The integrated
LVDlink transceivers support both LVD and SE signals and do not require
external transceivers. The LSI53C1020 supports the Ultra320 SCSI,
Ultra160 SCSI, Ultra2 SCSI, Ultra SCSI, and Fast SCSI interfaces.
2.4.1 Ultra320 SCSI Features
This section describes how the LSI53C1020 implements the features in
the SPI-4 draft specification.
2.4.1.1 Parallel Protocol Request (PPR)
A SCSI extended message negotiates the PPR parameters. The PPR
parameters include the (1) transfer period; (2) maximum REQ/ACK
offset; (3) QAS; (4) margin control settings (MCS); (5) transfer width;
(6) IU_Request; (7) write flow; (8) read streaming; (9) RTI;
(10) precompensation enable; (11) information unit transfers; and the
(12) DT data phases between an initiator and a target.
2.4.1.2 Double Transition (DT) Clocking
Ultra160 SCSI and Ultra320 SCSI implement DT clocking to provide
speeds up to 80 megatransfers per second (megatransfers/s) for
Ultra160 SCSI, and up to 160 megatransfers/s for Ultra320 SCSI. When
implementing DT clocking, a SCSI device samples data on both the
asserting and deasserting edge of REQ/ACK. DT clocking is only valid
using an LVD SCSI bus.
2.4.1.3 Intersymbol Interference (ISI) Compensation
ISI Compensation uses paced transfers and precompensation to enable
high data transfer rates. Ultra320 SCSI data transfers require
ISI Compensation.
Paced Transfers – The initiator and target must establish a paced
transfer agreement that specifies the REQ/ACK offset and the transfer
period before using this feature. Devices can only perform paced
transfers during Ultra320 SCSI DT data phases. In paced transfers, the