Scsi control zero (scntl0) – Avago Technologies LSI8751D User Manual
Page 119
5-3
Register: 0x00 (0x80)
SCSI Control Zero (SCNTL0)
Read/Write
ARB1[1:0]
Arbitration Mode Bits 1 and 0
[7:6]
Simple Arbitration
1. The LSI53C875 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 LSI53C875 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
LSI53C875 wins arbitration.
4. Once the LSI53C875 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.
Full Arbitration, Selection/Reselection
1. The LSI53C875 waits for a bus free condition.
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