DR805x Instructions set details
- 31 -
3.10.
DEC
DEC byte
Decrement byte
The variable indicated is decremented by 1. An original value of 00 H
will underflow to 0FF H. No flags are affected. Four operand addressing
modes are allowed: accumulator, register, direct, or register-indirect.
When this instruction is used to modify an output port, the value used
as the original port data will be read from the output data latch,
not
the
input pins.
Instruction:
Function:
Description:
Note:
3.10.1.
Operation:
DEC A
(PC)
←
(PC) + 1
(A)
←
(A) - 1
1
2
Bytes:
Cycles:
Encoding:
0
0
0
1
0
1
0
0
3.10.2.
Operation:
DEC R
N
(PC)
←
(PC) + 1
(Rn)
←
(Rn) - 1
1
3
Bytes:
Cycles:
Encoding:
0
0
0
1
1
r
r
r
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