7630 datasheet(187/238 Pages) RENESAS

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3-16

APPENDIX

3.3 Notes on use

7630 Group User’s Manual

NOP instruction

Set D flag to “1”

SEC, CLC, or CLD instruction

ADC or SBC instruction

(4) Execution of decimal calculations

The ADC and SBC are the only instructions which will yield proper decimal notation, set the decimal

mode flag (D) to “1” with the SED instruction. After executing the ADC or SBC instruction, execute

another instruction before executing the SEC, CLC, or CLD instruction.

(5) Notes on status flags in decimal mode

When decimal mode is selected, the values of

three of the flags in the status register (the N,

V, and Z flags) are invalid after a ADC or SBC

instruction is executed.

The carry flag (C) is set to “1” if a carry is

generated as a result of the calculation, or is

cleared to “0” if a borrow is generated. To

determine whether a calculation has generated

a carry, the C flag must be initialized to “0”

before each calculation. To check for a borrow,

the C flag must be initialezed to “1” before

each calculation.

(6) JPM instruction

When using the JMP instruction in indirect addressing mode, do not specify the last address on a

page as an indirect address.

(3) Detection of BRK instruction interrupt source

It can be detected that the BRK instruction

interrupt event or the least priority interrupt event

by referring the stored B flag state. Refer to

the stored B flag state in the interrupt routine.

Fig. 3.3.2 Interrupt routine

(S)

(S) + 1

PCL(Low-order of program counter)

PCH(High-order of program counter)

= B flag

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