LSI53C825AJ LSI, LSI53C825AJ Datasheet - Page 53

• Manufacturer Part Number: LSI53C825AJ
• Manufacturer: LSI

Specifications of LSI53C825AJ

• Lead Free Status / RoHS Status: Not Compliant

To interface the LSI53C825A to the 75LBC976, connect the DIR pins, as
well as IGS and TGS, of the LSI53C825A directly to the transceiver
enables (nDE/RE/). These signals control the direction of the channels
on the 75LBC976.
The SCSI bidirectional control and data pins (SD[7:0]/, SDP0/, REQ/,
ACK/, MSG/, I_O/, C_D/, and ATN/) of the LSI53C825A connect to the
bidirectional data pins (nA) of the 75LBC976 with a pull-up resistor. The
pull-up value should be no lower than the transceiver I
can tolerate,
OL
but not so high as to cause RC timing problems. The three remaining
pins, SEL/, BSY/, and RST/ are connected to the 75LBC976 with a
pull-down resistor. The pull-down resistors are required when the pins
(nA) of the 75LBC976 are configured as inputs. When the data pins are
inputs, the resistors provide a bias voltage to both the LSI53C825A pins
(SEL/, BSY/, and RST/) and the 75LBC976 data pins. Because the SEL/,
BSY/, and RST/ pins on the LSI53C825A are inputs only, this
configuration allows for the SEL/, BSY/, and RST/ SCSI signals to be
asserted on the SCSI bus. The differential pairs on the SCSI bus are
reversed when connected to the 75LBC976, due to the active low nature
of the SCSI bus.
8-Bit/16-Bit SCSI and the Differential Interface – In an 8-bit SCSI
bus, the SD[15:8] pins on the LSI53C825A should be pulled up with a
1.5 k
resistor or terminated like the rest of the SCSI bus lines. This is
very important, as errors may occur during reselection if these lines are
left floating. In the LSI53C825AJ, the SDIRP1 pin is replaced by the TCK
JTAG signal. If the device is used in a wide differential system, use the
SDIRP0 pin to control the direction of the differential transceiver for both
the SP0 and SP1 signals. The SDIRP0 signal is capable of driving both
direction inputs from a transceiver.
2.4.9.2 Terminator Networks
The terminator networks provide the biasing needed to pull signals to an
inactive voltage level, and to match the impedance seen at the end of
the cable with the characteristic impedance of the cable. Terminators
must be installed at the extreme ends of the SCSI chain, and only at the
ends; no system should ever have more or less than two terminators
installed and active. SCSI host adapters should provide a means of
PCI Cache Mode
2-29