Notes On Decimal Operation; Notes On Interrupts; Fig. 6.3.4 Note In Decimal Arithmetic Operation; Fig. 6.3.5 Execution Of Bbc Or Bbs Instruction - Renesas 7200 Series User Manual

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
instruction 1 , 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.
1: data transfer instructions: LDM, LDA, STA,
STX, and STY instructions

Fig. 6.3.4 Note in decimal arithmetic operation

Clear the interrupt request (request distinguish)
bit to "0" (no interrupt issued)

Fig. 6.3.5 Execution of BBC or BBS instruction

7220 Group User's Manual
APPENDIX
6.3 Notes on use
Set the decimal mode flag D
to "1"
Execute ADC or SBC instruction
Execute NOP instruction
Execute SEC, CLC, or CLD instruction
NOP (one or more instructions)
Execute BBC or BBS instruction
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