
5-16
SYM53C876/876E Data Manual
SCSI SCRIPTS Instruction Set
Transfer Control Instructions
Transfer Control
Instructions
First Dword
Bits 31-30 Instruction Type - Transfer Con-
trol Instruction
Bits 29-27 Op Code
This 3-bit field specifies the type of transfer
control instruction to execute. All transfer
control instructions can be conditional. They
can be dependent on a true/false comparison
of the ALU Carry bit or a comparison of the
SCSI information transfer phase with the
Phase field, and/or a comparison of the First
Byte Received with the Data Compare field.
Each instruction can operate in initiator or
target mode.
Jump Instruction
1. The SYM53C876 can do a true/false
comparison of the ALU carry bit, or compare
the phase and/or data as defined by the Phase
Compare, Data Compare and True/False bit
fields. If the comparisons are true, the it loads
the DSP register with the contents of the
DSPS register. The DSP register now
contains the address of the next instruction.
2. If the comparisons are false, the SYM53C876
fetches the next instruction from the address
pointed to by the DSP register, leaving the
instruction pointer unchanged.
Call Instruction
1. The SYM53C876 can do a true/false
comparison of the ALU carry bit, or compare
the phase and/or data as defined by the Phase
Compare, Data Compare, and True/False bit
fields. If the comparisons are true, it loads the
DSP register with the contents of the DSPS
register and that address value becomes the
address of the next instruction.
When the SYM53C876 executes a Call
instruction, the instruction pointer contained
in the DSP register is stored in the TEMP
register. Since the TEMP register is not a
stack and can only hold one dword, nested
call instructions are not allowed.
2. If the comparisons are false, the SYM53C876
fetches the next instruction from the address
pointed to by the DSP register and the
instruction pointer is not modified.
OPC2
OPC1
OPC0
Instruction Defined
0
0
0
0
1
0
0
1
1
X
0
1
0
1
X
Jump
Call
Return
Interrupt
Reserved