PM0223 datasheet(43/110 Pages) STMICROELECTRONICS

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PM0223

The STM32L0 Cortex-M0+ Instruction Set

Note:

For most instructions, the value of the PC is the address of the current instruction plus 4

bytes.

Your assembler might permit other syntaxes for PC-relative expressions, such as a label

plus or minus a number, or an expression of the form [PC,#imm].

3.3.6

Conditional execution

Most data processing instructions update the condition flags in the Application Program

Status Register (APSR) according to the result of the operation, see Application Program

Status Register on page 15. Some instructions update all flags, and some only update a

subset. If a flag is not updated, the original value is preserved. See the instruction

descriptions for the flags they affect.

You can execute a conditional branch instruction, based on the condition flags set in another

instruction, either:

•

Immediately after the instruction that updated the flags.

•

After any number of intervening instructions that have not updated the flags.

On the STM32L0 Cortex-M0+ processor, conditional execution is available by using

conditional branches.

This section describes:

•

The condition flags on page 43.

•

Condition code suffixes on page 44.

The condition flags

The APSR contains the following condition flags:

For more information about the APSR see Program Status Register on page 14.

A carry occurs:

•

If the result of an addition is greater than or equal to 232.

•

If the result of a subtraction is positive or zero.

•

As the result of a shift or rotate instruction.

Overflow occurs when the sign of the result, in bit[31], does not match the sign of the result

had the operation been performed at infinite precision, for example:

•

If adding two negative values results in a positive value.

•

If adding two positive values results in a negative value.

•

If subtracting a positive value from a negative value generates a positive value.

•

If subtracting a negative value from a positive value generates a negative value.

The Compare operations are identical to subtracting, for CMP, or adding, for CMN, except that

the result is discarded. See the instruction descriptions for more information.

Set to 1 when the result of the operation was negative, cleared to 0 otherwise

Set to 1 when the result of the operation was zero, cleared to 0 otherwise.

Set to 1 when the operation resulted in a carry, cleared to 0 otherwise.

Set to 1 when the operation caused overflow, cleared to 0 otherwise.

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