Scsi control zero (scntl0), Register: 0x00 – LSI 53C875A User Manual
Page 112
4-20
Registers
Register: 0x00
SCSI Control Zero (SCNTL0)
Read/Write
ARB[1:0]
Arbitration Mode Bits 1 and 0
[7:6]
Simple Arbitration
1. The LSI53C875A waits for a bus free condition to
occur.
2. It asserts SBSY/ and its SCSI ID (contained in the
register) onto the SCSI bus. If
the SSEL/ signal is asserted by another SCSI device,
the LSI53C875A deasserts SBSY/, deasserts its ID
and sets the Lost Arbitration bit (bit 3) in the
register.
3. After an arbitration delay, the CPU should read the
register to check if a
higher priority SCSI ID is present. If no higher priority
ID bit is set, and the Lost Arbitration bit is not set, the
LSI53C875A wins arbitration.
4. Once the LSI53C875A wins arbitration, SSEL/ must be
asserted using the
SCSI Output Control Latch (SOCL)
for a bus clear plus a bus settle delay (1.2
µ
s) before
a low level selection is performed.
7
6
5
4
3
2
1
0
ARB[1:0]
START
WATN
EPC
R
AAP
TRG
1
1
0
0
0
x
0
0
ARB1
ARB0
Arbitration Mode
0
0
Simple arbitration
0
1
Reserved
1
0
Reserved
1
1
Full arbitration, selection/reselection