PM0215 The STM32 Cortex-M0 instruction set
Doc ID 022979 Rev 1 53/91
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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