
Instruction Set of the I/O Processor
Transfer Control Instructions
6-16
SYM53C875/875E Data Manual
Transfer Control
Instructions
First Dword
Bits 31-30 Instruction Type - Transfer Control
Instruction
Bits 29-27 Op Code
T his 3-bit field specifies the type of transfer
control instruction to be executed. All transfer
control instructions can be conditional. T hey
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 tar-
get mode.
Jump Instruction
1. T he SYM53C875 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
SYM53C875 loads the DSP register with the
contents of the DSPS register. T he DSP
register now contains the address of the next
instruction.
2. If the comparisons are false, the SYM53C875
fetches the next instruction from the address
pointed to by the DSP register, leaving the
instruction pointer unchanged.
Call Instruction
1. T he SYM53C875 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
SYM53C875 loads the DSP register with the
contents of the DSPS register and that address
value becomes the address of the next
instruction.
When the SYM53C875 executes a Call
instruction, the instruction pointer contained
in the DSP register is stored in the T EMP reg-
ister. Since the T EMP register is not a stack
and can only hold one longword, nested call
instructions are not allowed.
2. If the comparisons are false, the SYM53C875
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