Avago Technologies LSI53C825AE - Manual (Page 210)

5-26 SCSI SCRIPTS Instruction Set
OPC[2:0] Opcode [29:27]
The combinations of these bits determine if the
instruction is a Read/Write or an I/O instruction. Opcodes
0b000 through 0b100 are considered I/O instructions.
O[2:0] Operator [26:24]
These bits are used in conjunction with the opcode bits
to determine which instruction is currently selected. Refer
to
Table 5.1 for field definitions.
D8 Use data8/SFBR 23
When this bit is set, SCSI First Byte Received (SFBR) is
used instead of the data8 value during a
Read-Modify-Write instruction (see
Table 5.1 ). This
allows the user to add two register values.
A[6:0] Register Address - A[6:0] [22:16]
It is possible to change register values from SCRIPTS in
read-modify-write cycles or move to/from
SCSI First Byte
Received (SFBR) cycles. A[6:0] selects an 8-bit
source/destination register within the LSI53C825A.
ImmD Immediate Data [15:8]
This 8-bit value is used as a second operand in logical
and arithmetic functions.
R Reserved [7:0]
5.5.2 Second Dword
Destination Address [31:0]
This field contains the 32-bit destination address where
the data is to move.
5.5.3 Read-Modify-Write Cycles
During these cycles the register is read, the selected operation is
performed, and the result is written back to the source register.
The Add operation is used to increment or decrement register values (or
memory values if used in conjunction with a Memory-to-Register Move
operation) for use as loop counters.