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APPENDIX
B.3 Special Instructions
This section describes the special instructions used for other than addressing.
■ Special instructions
●
JMP @A
This instruction sets the contents of A (accumulator) to PC (program counter) as the address, and causes a
branch to that address. One of the N branch destination addresses is selected from a table, and then
transferred to A. The instruction can be executed to perform N-branch processing.
Figure B.3-1 "JMP @A" shows a summary of the instruction.
Figure B.3-1 JMP @A
●
MOVW A, PC
This instruction performs the operation which is the reverse of that performed by JMP @A. That is, the
instruction stores the contents of PC in A. When the instruction is executed in the main routine, so that a
specific subroutine is called, whether A contains a predetermined value can be checked by the subroutine.
This can be used to determine that the branch source is not any unexpected section of the program and to
check for program runaway.
Figure B.3-2 "MOVW A, PC" shows a summary of the instruction.
Figure B.3-2 MOVW A, PC
After the MOVW A, PC instruction is executed, A contains the address of the operation code of the next
instruction, rather than the address of the operation code of MOVW A, PC. Accordingly, Figure B.3-2
"MOVW A, PC" shows that A contains 1234
H
, which is the address of the operation code of the instruction
that follows MOVW A, PC.
1 2 3 4H
A
X X X X
H
Previous PC
A
Current PC
(Before execution) (After execution)
1 2 3 4
H
1 2 3 4H
A A
X X X XH
1 2 3 4H 1 2 3 4H
1 2 3 4H
Previous PC
Current PC