D17133CS datasheet(261/289 Pages) NEC

261 / 289 page

CHAPTER 18

INSTRUCTION SET

246

<3> Example

Executes the RET instruction, if the LSB (least significant bit) content for address 25H in the data memory

(RAM) is 0. The execution is returned to the instruction next to the CALL instruction. If the LSB is 1, executes

the RETSK instruction. The execution is returned to the instruction following the one next to the CALL

instruction (in this example, ADD 03H, 16H).

CALL

ADD

SUB1

LOOP

03H, 16H

SUB1

SKF

RETSK

RET

25H, #0001B

; LSB of 25H is "1"

; LSB of 25H is "0"

(5)

RETI

Return to the main program from interrupt service routine

<1> OP code

00111

100

1110

0000

<2> Function

← ASR, INTR ← INTSK, SP ← SP+1

Instruction to return to the main program, from an interrupt service program.

Restores the return address, saved to the stack by a vector interrupt, to the program counter.

Part of the system register is also returned to the status before the occurrence of the vector interrupt.

<3> Note 1

The system register contents that are automatically saved (i.e., that can be restored by the RETI instruction)

when an interrupt occurs is PSWORD.

Note 2

If the RETI instruction is used, instead of the RET instruction, in an ordinary subroutine, the contents of the

bank (which are to be saved when an interrupt occurs) are changed to the contents of the interrupt stack,

when the execution has returned to the return address. Consequently, an unpredictable status may be

assumed. Therefore, use the RET (or RETSK) instruction to return from a subroutine.

D17133CS Datasheet(PDF) 261 Page - NEC