M38044F2HKP datasheet(331/387 Pages) RENESAS

331 / 387 page

3-41

REJ09B0212-0100Z

Rev.1.00

Jan 14, 2005

3804 Group (Spec.H)

APPENDIX

3.3 Notes on use

➁ How to reference the processor status register

To reference the contents of the processor status register (PS), execute the PHP instruction once

then read the contents of (S+1). If necessary, execute the PLP instruction to return the PS to its

original status.

A NOP instruction should be executed after every PLP instruction.

Fig. 3.3.7 Stack memory contents after PHP

instruction execution

Fig. 3.3.6 Sequence of PLP instruction execution

PLP instruction execution

↓

NOP

(2)

BRK instruction

➀ Interrupt priority level

When the BRK instruction is executed with the following conditions satisfied, the interrupt execution

is started from the address of interrupt vector which has the highest priority.

• Interrupt request bit and interrupt enable bit are set to “1”.

• Interrupt disable flag (I) is set to “1” to disable interrupt.

(3)

Decimal calculations

➀ 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.

➁ Notes on status flag 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

initialized to “1” before each calculation.

(S)

(S)+1

Stored PS

Set D flag to “1”

↓

ADC or SBC instruction

↓

NOP instruction

↓

SEC, CLC, or CLD instruction

Fig. 3.3.8 Status flag at decimal calculations

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