1 first dword, First dword – LSI 53C875A User Manual
Page 214
5-14
SCSI SCRIPTS Instruction Set
5.4.1 First Dword
IT[1:0]
Instruction Type - I/O Instruction
[31:30]
The IT bit configuration (01) defines an I/O Instruction
Type.
OPC[2:0]
OpCode
[29:27]
The OpCode bit configurations define the I/O operation
performed but the OpCode bit meanings change in Target
mode compared to Initiator mode. OpCode bit
configurations (101, 110, and 111) are considered
Read/Write instructions, and are described in
5.5, “Read/Write Instructions.”
This section describes
Target mode operations.
Target Mode
Reselect Instruction
The LSI53C875A arbitrates for the SCSI bus by asserting
the SCSI ID stored in the
register.
If it loses arbitration, it tries again during the next
available arbitration cycle without reporting any lost
arbitration status.
If the LSI53C875A wins arbitration, it attempts to reselect
the SCSI device whose ID is defined in the destination ID
field of the instruction. Once the LSI53C875A wins
arbitration, it fetches the next instruction from the address
pointed to by the
register.
31 30 29
27 26 25 24 23
20 19
16 15
11 10
9
8
7
6
5
4
3
2
0
Register
Register
IT[1:0] OPC[2:0] RA TI Sel
R
ENDID[3:0]
R
CC TM
R
ACK
R
ATN
R
0
1
x
x
x
x
x
x
0
0
0
0
x
x
x
x
0
0
0
0
0
x
x
0
0
x
0
0
x
0
0
0
OPC2 OPC1 OPC0
Instruction Defined
0
0
0
Reselect
0
0
1
Disconnect
0
1
0
Wait Select
0
1
1
Set
1
0
0
Clear