Avago Technologies LSI53C1030 - Manual (Page 51)

Ultra320 SCSI Functional Description 2-21
Version 2.2 Copyright © 2001, 2002, 2003 by LSI Logic Corporation. All rights reserved.
Figure 2.3 Example of Precompensation
2.4.1.4 Packetized Transfers
Packetized transfers are also referred to as information unit transfers.
They reduce overhead on the SCSI bus by merging several of the SCSI
bus phases. Packetized transfers can only occur in DT Data phases. The
initiator and target must establish either a DT synchronous transfer
agreement or a paced transfer agreement before performing packetized
transfers.
The number of bytes in an information unit transfer is always a multiple
of four. If the number of bytes to transfer in the information unit is not a
multiple of four, the LSI53C1030 transmits pad bytes to bring the byte
count to a multiple of four.
2.4.1.5 Quick Arbitration and Selection (QAS)
When using packetized transfers, QAS allows devices to arbitrate for the
bus immediately after the message phase. QAS reduces the bus
Normal Drive Strength
Boosted Drive Strength Normal Drive Strength
a. Drivers with Precompensation Disabled
b. Drivers with Precompensation Enabled