Table 2.5 differential mode, Differential mode – Avago Technologies LSI53C876E User Manual
Page 47
SCSI Functional Description
2-25
ATN/, SD[15:0], and SDP[1:0]/ signals is 1.5 k
Ω
. In addition to the
standard SCSI lines, the following signals defined in
are used
during differential operation by the LSI53C876:
See
for an example differential wiring diagram, in which the
LSI53C876 is connected to the TI SN75976A differential transceiver. The
recommended value of the pull-up resistor on the REQ/, ACK/, MSG/,
C/D/, I/O/, ATN/, SD[15:0]/, SDP0/, and SDP1/ lines is 680
Ω
when the
Active Negation portion of LSI Logic TolerANT technology is not enabled.
When TolerANT technology is enabled, the recommended resistor value
on the REQ/, ACK/, SD[7:0]/, and SDP0/ signals is 1.5 k
Ω.
The electrical
characteristics of these pins change when TolerANT is enabled,
permitting a higher resistor value.
To interface the LSI53C876 to the SN75976A, connect the DIR pins, as
well as IGS and TGS, of the LSI53C876 directly to the transceiver
enables (nDE/RE/). These signals control the direction of the channels
on the SN75976A.
The SCSI bidirectional control and data pins (SD[15:0]/, SDP0/, SDP1/,
REQ/, ACK/, MSG/, I_O/, C_D/, and ATN/) of the LSI53C876 connect to
the bidirectional data pins (nA) of the SN75976A with a pull-up resistor.
The three remaining pins, SEL/, BSY/, and RST/ are connected to the
SN75976A with a pull-down resistor. The pull-down resistors are required
Table 2.5
Differential Mode
Signal
Function
BSYDIR, SELDIR,
RSTDIR
Active HIGH signals used to enable the differential drivers as outputs for SCSI
signals BSY/, SEL/, and RST/, respectively.
SDIR[15:0],
SDIRP[1:0]
Active HIGH signals used to control direction of the differential drivers for SCSI
data and parity lines, respectively.
IGS
Active HIGH signal used to control direction of the differential driver for initiator
group signals ATN/ and ACK/.
TGS
Active HIGH signal used to control direction of the differential drivers for target
group signals MSG/, C/D/, I/O/, and REQ/.
DIFFSENS
Input to the LSI53C876 used to detect the presence of an SE device on a
differential system. If a logical zero is detected on this pin, then it is assumed
that an SE device is on the bus and all SCSI outputs will be 3-stated to avoid
damage to the transceiver.