PM0215 Datasheet, PDF (58/91 Pages) STMicroelectronics – STM32F0xxx Cortex-M0 programming manual

The STM32 Cortex-M0 instruction set
PM0215
3.5.9
TST
Test bits.
Syntax
TST Rn, Rm
where:
● ‘Rn’ is the register holding the first operand
● ‘Rm’ is the register to test against.
Operation
This instruction tests the value in a register against another register. It updates the condition
flags based on the result, but does not write the result to a register.
The TST instruction performs a bitwise AND operation on the value in Rn and the value in
Rm. This is the same as the ANDS instruction, except that it discards the result.
To test whether a bit of Rn is 0 or 1, use the TST instruction with a register that has that bit
set to 1 and all other bits cleared to 0.
Restrictions
In these instructions, Rn and Rm must only specify R0-R7.
Condition flags
This instruction:
● Updates the N and Z flags according to the result
● Does not affect the C or V flag
Examples
TST R0, R1
; Perform bitwise AND of R0 value and R1 value,
; condition code flags are updated but result is discarded
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Doc ID 022979 Rev 1