NEC 78K/0 Series - Manual (Page 72)

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CHAPTER 5 EXPLANATION OF INSTRUCTIONS
User's Manual U12326EJ4V0UM
Decrement
DEC
Byte Data Decrement
[Instruction format] DEC dst
[Operation] dst ← dst – 1
[Operand]
Mnemonic Operand(dst)
DEC r
saddr
[Flag]
Z AC CY
Ч Ч
[Description]
• The destination operand (dst) contents are decremented by only one.
• If the decrement result is 0, the Z flag is set (1). In all other cases, the Z flag is cleared (0).
• If the decrement generates a carry for bit 3 out of bit 4, the AC flag is set (1). In all other cases, the AC
flag is cleared (0).
• Because this instruction is frequently used for decrement of a counter for repeated operations and an indexed
addressing offset register, the CY flag contents are not changed (to hold the CY flag contents in multiple-
byte operation).
• If dst is the B or C register or saddr, and it is not desired to change the AC and CY flag contents, the DBNZ
instruction can be used.
[Description example]
DEC FE92H; The contents at address FE92H are decremented.