Texas Instruments MSC1210 manual Incrementing and Decrementing Registers INC, DEC

Models: MSC1210

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Incrementing and Decrementing Registers (INC, DEC)

16.10 Incrementing and Decrementing Registers (INC, DEC)

Two instructions, INC and DEC, can be used to increment or decrement the value of a register, internal RAM, or SFR by 1. These instructions are rather self-explanatory.

The INC instruction will add 1 to the current value of the specified register. If the current value is 255, it will overflow back to 0. For example, if the accumula- tor holds the value 240 and the INC A instruction is executed, the accumulator is incremented to 241.

INC A ;Increment the accumulator by 1

INC R1 ;Increment R1 by 1

INC 40h ;Increment Internal RAM address 40h by 1

The DEC instruction will subtract 1 from the current value of the specified regis- ter. If the current value is 0, it will underflow back to 255. For example, if the accumulator holds the value 240 and the DEC A instruction is executed, the accumulator will be decremented to 239.

DEC A ;Decrement the accumulator by 1

DEC R1 ;Decrement R1 by 1

DEC 40h ;Decrement Internal RAM address 40h by 1

Note:

Under some assembly language architectures, the INC and DEC instruc- tions set an overflow or underflow flag when the register overflows from 255 to 0 or underflows from 0 back to 255, respectively. This is not the case with the INC and DEC instructions in 8052 assembly language. Neither of these instructions affects any flags whatsoever.

8052 Assembly Language

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Texas Instruments MSC1210 manual Incrementing and Decrementing Registers INC, DEC