Avago Technologies LSI53C180 - Manual (Page 28)

2-10 Functional Descriptions
6. The last stage develops pull-up and pull-down signals with drive and
3-state control.
7. A parallel function ensures that bus (transmission line) recovery
occurs for a specified time after the last signal deassertion on each
signal line.
2.1.7.7 Control/Data, Input/Output, Message, and Attention Controls
(SCD, SIO, SMSG, and SATN)
A_SCD, A_SIO, A_SMSG, A_SATN, B_SCD, B_SIO, B_SMSG, and
B_SATN are control signals that have the following processing steps:
1. The input signal is blocked if it is being driven by the LSI53C180.
2. The next stage is a leading edge filter. This ensures the output does
not switch for a specified time after the leading edge. The duration
of the input signal determines the duration of the output.
3. The final stage develops pull-up and pull-down controls for the SCSI
I/O logic, including 3-state controls for the pull-up.
4. A parallel function ensures that bus (transmission line) recovery is for
a specified time after the last signal deassertion on each signal line.
2.1.7.8 Multimode Signal Control
A_SD[15:0], A_SDP[1:0], A_SBSY, A_SSEL, A_SCD, A_SIO, A_SMSG,
A_SREQ, A_SACK, A_SATN, A_SRST, B_SD[15:0], B_SDP[1:0],
B_SBSY, B_SSEL, B_SCD, B_SIO, B_SMSG, B_SREQ, B_SACK,
B_SATN, and B_SRST are all multimode signals. The mode is controlled
by the voltage sensed at the DIFFSENS input. The A and B Sides are
independently controlled.
When the correct DIFFSENS voltage selects SE mode, the plus signal
leads are internally tied to ground and the minus SCSI signals are the
SE input/outputs.
When the correct DIFFSENS voltage selects LVD mode, the plus and
minus signal leads are the differential signal pairs.
A transition from any mode to another mode causes a SCSI RST to be
asserted on the opposite SCSI bus as a notification of state change.