Scsi control zero (scntl0) – Avago Technologies LSI53C825AE User Manual
Page 108
4-20
Registers
Register: 0x00 (0x80)
SCSI Control Zero (SCNTL0)
Read/Write
ARB[1:0]
Arbitration Mode Bits 1 and 0
[7:6]
Simple Arbitration
1.
The LSI53C825A 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 LSI53C825A 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 LSI53C825A has won arbitration.
4.
Once the LSI53C825A has won arbitration, SSEL/
must be asserted using the
for a bus clear plus a bus settle delay
(1.2
µ
s) before a low level selection can be
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