PM0215 datasheet(53/91 Pages) STMICROELECTRONICS

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PM0215

The STM32 Cortex-M0 instruction set

Doc ID 022979 Rev 1

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3.5.4

CMP and CMN

Compare and compare negative.

Syntax

CMN Rn, Rm

CMP Rn, #imm

CMP Rn, Rm

where:

●

‘Rn’ is the register holding the first operand

●

Rm is the register to compare with.

●

imm is the immediate value to compare with.

Operation

These instructions compare the value in a register with either the value in another register or

an immediate value. They update the condition flags on the result, but do not write the result

to a register.

The CMP instruction subtracts either the value in the register specified by Rm, or the

immediate imm from the value in Rn and updates the flags. This is the same as a SUBS

instruction, except that the result is discarded.

The CMN instruction adds the value of Rm to the value in Rn and updates the flags. This is

the same as an ADDS instruction, except that the result is discarded.

Restrictions

In these instructions:

●

CMN instruction Rn, and Rm must only specify R0-R7.

●

CMP instruction:

–

Rn and Rm can specify R0-R14

–

imm must be in the range 0-255.

Condition flags

These instructions update the N, Z, C and V flags according to the result.

Examples

CMP R2, R9

CMN R0, R2

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