Avago Technologies LSI53C825AE - Manual (Page 208)

5-24 SCSI SCRIPTS Instruction Set
5.5 Read/Write Instructions
The Read/Write instruction supports addition, subtraction, and
comparison of two separate values within the chip. It performs the
desired operation on the specified register and the
SCSI First Byte
Received (SFBR) register, then stores the result back to the specified
register or the SFBR.
5.5.1 First Dword
IT[1:0] Instruction Type - Read/Write Instruction [31:30]
The configuration of the IT bits, the Opcode bits and the
Operator bits define the Read/Write Instruction Type. The
configuration of all these bits determine which instruction
is currently selected.
Figure 5.4 illustrates the Read/Write Instruction register.