DR805X Datasheet, PDF(31/79 Page) Digital Core Design – 8-bit RISC Microcontroller Instructions set details ver 3.10

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DR805X Datasheet, PDF (31/79 Pages) Digital Core Design – 8-bit RISC Microcontroller Instructions set details ver 3.10

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DR805x Instructions set details

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3.10. DEC

Instruction: DEC byte

Function: Decrement byte

Description: 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.

Note:

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.

3.10.1.

DEC A

Operation: (PC) â (PC) + 1

(A) â (A) - 1

Bytes:

Cycles:

Encoding:

00010100

3.10.2.

DEC RN

Operation: (PC) â (PC) + 1

(Rn) â (Rn) - 1

Bytes:

Cycles:

Encoding:

00011 r r r

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