Avago Technologies LSI53C876E - Manual (Page 46)

2-24 Functional Description
Figure 2.4 shows how data is moved to/from the SCSI bus in each of the
different modes.
Figure 2.4 LSI53C876 Host Interface SCSI Data Paths
2.2.7 SCSI Bus Interface
All SCSI signals are active LOW. The LSI53C876 contains the SE output
drivers and can be connected directly to the SCSI bus. Each output is
isolated from the power supply to ensure that a powered-down
LSI53C876 has no effect on an active SCSI bus (CMOS “voltage
feed-through” phenomena). TolerANT technology provides signal filtering
at the inputs of SREQ/ and SACK/ to increase immunity to signal
reflections.
2.2.7.1 Differential Mode
In differential mode, the SDIR[15:0], SDIRP[1:0], IGS, TGS, RSTDIR,
BSYDIR, and SELDIR signals control the direction of external differential
pair transceivers. The LSI53C876 is placed in differential mode by setting
the DIF bit, bit 5 of the
SCSI Test Two (STEST2) register (0x4E). Setting
this bit 3-states the BSY/, SEL/, and RST/ pads so they can be used as
pure input pins. When TolerANT active negation is enabled, the
recommended resistor value on the REQ/, ACK/, MSG/, C_D/, I_O/,
PCI Interface
DMA FIFO
(32 Bits x 134)
SODL Register
SCSI Interface
PCI Interface
DMA FIFO
(32 Bits x 134)
SIDL Register
SCSI Interface
PCI Interface
DMA FIFO
(32 Bits x 134)
SODL Register
SCSI Interface
SODR Register
PCI Interface
DMA FIFO
(32 Bits x 134)
SCSI Interface
SCSI FIFO
(8 or 16 Bits x 16)
Asynchronous
SCSI Send
Asynchronous
SCSI Receive
Synchronous
SCSI Send
Synchronous
SCSI Receive
SWIDE Register SWIDE Register