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
Содержание Symbios SYM53C040
Страница 12: ...xii Preface...
Страница 90: ...4 18 SCSI and DMA Registers...
Страница 98: ...5 8 SFF 8067 Registers...
Страница 110: ...6 12 Two Wire Serial Registers...
Страница 126: ...7 16 Miscellaneous Registers...
Страница 160: ...8 34 System Registers...
Страница 184: ...9 24 Electrical Characteristics...
Страница 194: ...A 10 Register Summary...
Страница 214: ......