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Table 4.2
Bus Phase
Data Out
Undefined
Command
Message Out
Data In
Undefined
Status
Message In
Register: 0xFC04
Current SCSI Bus Status (CSBS)
Read Only
7
6
RST
BSY
x
x
The Current SCSI Bus Status register is a read only register that
monitors seven SCSI bus control signals plus the data bus parity bit. For
example, an initiator device can use this register to determine the current
bus phase and to poll REQ/ for pending data transfers. The SCSI bus
status information in this register may also help determine why a
particular interrupt occurred.
RST
SCSI Reset
BSY
Busy
REQ
Request
MSG
Message
C_D
Command/Data
I_O
Input/Output
SCSI Phase Bit Values
Assert MSG/ Assert CD/
0
1
0
1
0
1
0
1
5
4
3
REQ
MSG
C_D
Defaults:
x
x
x
Assert IO/
0
0
0
0
1
0
1
0
0
1
0
1
1
1
1
1
2
1
0
I_O
SEL
DBP
x
x
x
7
6
5
4
3
2
4-9
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