Avago Technologies LSI53C1000R - Manual (Page 53)

SCSI Functional Description 2-23
Version 2.2 Copyright © 2000–2003 by LSI Logic Corporation. All rights reserved.
If the commands complete successfully with no CRC errors, bus hangs,
or data pattern errors, then the negotiated speed is valid.
CRC – CRC is the error detecting code used in Ultra160 SCSI. Four
bytes are transferred with data to increase the reliability of data transfers.
CRC is used in the DT Data-In and DT Data-Out phases only. Because
CRC is implied with DT mode and only works with DT mode, the DT
setting can be used for CRC.
DT Clocking – Ultra160 SCSI implements DT clocking to provide
speeds up to 80 megatransfers/s. DT clocking means that the data is
sampled on both the asserting and deasserting edge of REQ/ACK.
DT clocking is only valid using a LVD SCSI bus.
In order to support DT clocking, there are two new phases for the SCSI
bus. The old Data-In and Data-Out phases are now called single
transition (ST) Data-In and ST Data-Out. The new phases are DT Data-In
and DT Data-Out. The use of DT and ST phases implies that the
SCRIPTS engine may use a different jump point for DT or ST.
Table 2.3
illustrates SCSI signal configuration for these phases.
To indicate DT or ST mode, a bit is set in the current “selection” data
reserved byte. BMOVE instructions identify the current BMOVE as either
DT or ST through the phase bits.
Table 2.3 New Phases on SCSI Bus
Phase MSG C/D I/O Description
ST Data-Out 0 0 0 –
ST Data-In 0 0 1 –
DT Data-Out 1 0 0 Previously reserved
DT Data-In 1 0 1 Previously reserved