Avago Technologies LSI53C140 - Manual (Page 24)

2-6 Functional Descriptions
Ver. 2.1 Copyright © 1998–2001 by LSI Logic Corporation. All rights reserved.
2.1.6 Dynamic Transmission Mode Changes
Any dynamic mode change (SE/LVD/HVD) on a bus segment is
considered to be a significant event that requires the initiator to
determine whether the mode change meets the requirements for that bus
segment.
The LSI53C140 supports dynamic transmission mode changes by
notifying the initiator(s) of changes in transmission mode (SE/LVD/HVD)
on A or B side segments by using SCSI bus RESET. The DIFFSENS line
detects a valid mode switch on the bus segments. After the DIFFSENS
state is present for 100 ms, the LSI53C140 generates a SCSI reset on
the opposite bus from the one that the transmission mode change
occurred on. This reset informs any initiators residing on the opposite
segment about the change in the transmission mode. Then, the
initiator(s) renegotiates synchronous transfer rates with each device on
that segment to ensure that there is a valid bus segment for that mode.
2.2 SCSI Signal Descriptions
Figure 2.2 shows the LSI53C140 signal grouping. A description of the
signal groups follows. For a description of a specific signal, refer to
Section 3.1, “General Description,” in Chapter 3 . For information about
signal electrical characteristics, refer to Section 3.2, “Electrical
Characteristics,” in Chapter 3 . For SCSI bus signal timing, see
Section 3.2.4, “SCSI Interface Timing,” in Chapter 3 .