7220 datasheet(224/303 Pages) RENESAS

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7220 Group User’s Manual

APPENDIX

6.3 Notes on use

6-5

6.3.2 Notes on decimal operation

(1)

How to execute arithmetic operation

instructions in decimal operation mode

To calculate in decimal notation, set the decimal

operation mode flag (D) to “1” by using the

SED instruction, and execute the ADC and

SBC instructions. After that, execute at least

one instruction to execute the SEC, CLC, or

CLD instruction.

(2)

Status flags in decimal operation mode

When the ADC or SBC instruction are executed

in decimal operation mode (D flag = “1”), the

N, V, and Z flags are invalid.

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

occurs as a result of an arithmetic operation,

or is cleared to “0” when a borrow occurs.

Therefore, the carry flag can be used to

determine whether a carry or a borrow has

occurred or not. Be sure to initialize the C

flag before each arithmetic operation.

6.3.3 Notes on Interrupts

(1) Executing BBC or BBS instruction

When executing the BBC or BBS instruction

to an interrupt request bit immediately after

this bit is set to “0” by using a data transfer

instructionV1, execute one or more instructions

before executing the BBC or BBS instruction.

Reason

If the BBC or BBS instruction is executed

immediately after an interrupt request bit of

an interrupt request register is cleared to “0,”

the value of the interrupt request bit before

being cleared to “0” is read.

V1: data transfer instructions: LDM, LDA, STA,

STX, and STY instructions

Clear the interrupt request (request distinguish)

bit to “0” (no interrupt issued)

NOP (one or more instructions)

Execute BBC or BBS instruction

Fig. 6.3.5 Execution of BBC or BBS instruction

Fig. 6.3.4 Note in decimal arithmetic operation

Set the decimal mode flag D

to “1”

Execute ADC or SBC instruction

Execute NOP instruction

Execute SEC, CLC, or CLD instruction

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