Avago Technologies LSI53C180 - Manual (Page 23)

Interface Signal Descriptions 2-5
2.1.5 DIFFSENS Receiver
The LSI53C180 contains LVD DIFFSENS receivers that detect the
voltage level on the A Side or B Side DIFFSENS lines to inform the
LSI53C180 of the transmission mode being used by the SCSI buses. A
device does not change its present signal driver or receiver mode based
on the DIFFSENS voltage levels unless a new mode is sensed
continuously for at least 100 ms.
Transmission mode detection for SE or LVD is accomplished through the
use of the DIFFSENS lines.
Table 2.1 shows the voltages on the
DIFFSENS lines and modes they will cause.
2.1.6 Dynamic Transmission Mode Changes
Any dynamic mode change (SE/LVD) 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 LSI53C180 supports dynamic transmission mode changes by
notifying the initiator(s) of changes in transmission mode (SE/LVD) on A
or B Side segments by using the 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 LSI53C180 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. The initiator(s) then
renegotiates synchronous transfer rates with each device on that segment.
2.1.7 SCSI Signal Descriptions
For a description of a specific signal, see Section 3.1, “Signal
Descriptions,” in Chapter 3 . For signal electrical characteristics, see
Section 3.2, “Electrical Characteristics.” For SCSI bus signal timing, see
Table 2.1 DIFFSENS Voltage Levels
Voltage Mode
−
0.35 to +0.5 SE
+0.7 to +1.9 LVD