2-36
Functional Description
2.2.13.2 HVD Mode
To maintain backward compatibility with legacy systems, the LSI53C896
can operate in the HVD mode (when the chip is connected to external
differential transceivers). In the HVD mode, the SD[15:0]+, SDP[1:0]+,
SREQ+, SACK+, SRST+, SBSY+, and SSEL+ signals control the
direction of external differential pair transceivers. The LSI53C896 is
placed in the HVD mode by setting the DIF bit, bit 5, of the
register (0x4E). Setting this bit 3-states the SBSY
−
,
SSEL
−
, and SRST
−
pads so they can be used as pure input pins. In
addition to the standard SCSI lines, the signals shown in
are
used by the LSI53C896 during HVD operation.
In the example differential wiring diagram in
, the LSI53C896 is
connected to TI SN75976 differential transceivers for Ultra SCSI operation.
The recommended value of the pull-up resistor on the SREQ
−
, SACK
−
,
SMSG
−
, SC_D
−
, SI_O
−
, SATN
−
, SD[7:0]
−
, and SDP0
−
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 SREQ
−
, SACK
−
, SD[7:0]
−
, and SDP0
−
signals is
1.5 k
Ω
. The electrical characteristics of these pins change when TolerANT
technology is enabled, permitting a higher resistor value.
Table 2.6
HVD Signals
Signal
Function
SBSY+, SSEL+,
SRST+
Active HIGH signals used to enable the differential drivers as outputs for
SCSI signals SBSY
−
, SSEL
−
, and SRST
−
, respectively.
SD[15:0]+,
SDP[1:0]+
Active HIGH signals used to control the direction of the differential drivers for
SCSI data and parity lines, respectively.
SACK+
Active HIGH signal used to control the direction of the differential drivers for
the initiator group signals SATN
−
and SACK
−
.
SREQ+
Active HIGH signal used to control the direction of the differential drivers for
target group signals SMSG
−
, SC_D
−
, SI_O
−
and SREQ
−
.
DIFFSENS
Input to the LSI53C896 used to detect the voltage level of a SCSI signal to
determine whether it is a SE, LVD, or HVD signal. The encoded result is
displayed in
bits 7 and 6.
*
Содержание LSI53C896
Страница 6: ...vi Preface...
Страница 16: ...xvi Contents...
Страница 88: ...2 62 Functional Description...
Страница 112: ...3 24 Signal Descriptions...
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Страница 338: ...6 70 Specifications Figure 6 40 LSI53C896 329 BGA Bottom View...
Страница 340: ...6 72 Specifications...
Страница 346: ...A 6 Register Summary...
Страница 362: ...IX 12 Index...