7477 datasheet(283/361 Pages) RENESAS

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2-57

7470/7471/7477/7478 GROUP USER’S MANUAL

APPLICATION

2.10 Notes on programming

7470

7471

7477

7478

2.10.2 Decimal calculations

(1) Execution of decimal calculations

The ADC and SBC are the only instructions

which will yield proper decimal results in decimal

mode. To calculate in 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.

(2) Note on 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 bor-

row, the C flag must be initialized before each

calculation.

Fig. 2.10.4 Note for decimal operation

2 For other notes, refer to the notes described in

each section.

Set D Flag to “1”

ADC or SBC instruction

NOP instruction

SEC, CLC, or CLD instruction

7477 Datasheet(PDF) 283 Page - Renesas Technology Corp