4-9
Register: 0xFC04
Current SCSI Bus Status (CSBS)
Read Only
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
7
BSY
Busy
6
REQ
Request
5
MSG
Message
4
C_D
Command/Data
3
I_O
Input/Output
2
Table 4.2
SCSI Phase Bit Values
Bus Phase
Assert MSG/ Assert CD/
Assert IO/
Data Out
0
0
0
Undefined
1
0
0
Command
0
1
0
Message Out
1
1
0
Data In
0
0
1
Undefined
1
0
1
Status
0
1
1
Message In
1
1
1
7
6
5
4
3
2
1
0
RST
BSY
REQ
MSG
C_D
I_O
SEL
DBP
Defaults:
x
x
x
x
x
x
x
x
Summary of Contents for Symbios SYM53C040
Page 12: ...xii Preface...
Page 90: ...4 18 SCSI and DMA Registers...
Page 98: ...5 8 SFF 8067 Registers...
Page 110: ...6 12 Two Wire Serial Registers...
Page 126: ...7 16 Miscellaneous Registers...
Page 160: ...8 34 System Registers...
Page 184: ...9 24 Electrical Characteristics...
Page 194: ...A 10 Register Summary...
Page 214: ......