Avago Technologies LSI53C120 - Manual (Page 27)

SCSI Signal Descriptions 2-9
Every B-side signal requires a driver enable control to allow for all the
possible signal conditions including SCAM support. The data bits require
individual controls for the selection phase of SCSI bus protocol.
Table 2.1
shows the Direction Control Signals to illustrate their possible signal
levels, states and subsequent effects.
2.2.7 Differential Mode (DIFF_MODE/)
This input informs the LSI53C120 that external differential transceivers
are used in this particular application. In addition, this input causes
internal logic to adjust for external differential control.
Table 2.2 shows
the DIFF_MODE/ control signal polarity to illustrate its possible signal
levels, states and subsequent effects.
2.2.8 Differential Sense (DIFF_SENSE)
This input signal determines if a single-ended device is placed on the
differential bus. If a single-ended source is detected, the differential
B-side is disabled and no differential B-side signals are driven. This
mechanism prevents potential damage to the HVD transceivers.
Table 2.1 Direction Control Signals (B_SDIR(15-0, P0, P1),
B_BSYDIR, B_SELDIR, B_CD_DIR, B_IO_DIR,
B_MSGDIR, B_REQDIR, B_ACKDIR, B_ATNDIR and
B_RSTDIR) Polarities
Signal Level State Effect
HIGH = 1 Asserted Drive LSI53C120 signals onto Bus B
LOW = 0 Deasserted Input Bus B signals to LSI53C120
Table 2.2 DIFF_MODE/ Control Signal Polarity
Signal Level State Effect
LOW = 0 Asserted Differential Signals and Controls are
enabled from the LSI53C120
HIGH = 1 Deasserted LSI53C120 Bus B drivers function in
single-ended mode