PM0215 datasheet(59/91 Pages) STMICROELECTRONICS

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PM0215

The STM32 Cortex-M0 instruction set

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3.6

Branch and control instructions

Table 21 shows the branch and control instructions:

3.6.1

B, BL, BX, and BLX

Branch instructions.

Syntax

B{cond} label

BL label

BX Rm

BLX Rm

where:

●

‘B’ is branch (immediate).

●

‘BL’ is branch with link (immediate).

●

‘BX’ is branch indirect (register).

●

‘BLX’ is branch indirect with link (register).

●

‘label’ is a PC-relative expression. See PC-relative expressions on page 39.

●

‘Rm’ is a register that indicates an address to branch to.

●

’Cond’ is an optional condition code, see Conditional execution on page 39.

Operation

All these instructions cause a branch to label, or to the address indicated in Rm. In addition:

●

The BL and BLX instructions write the address of the next instruction to LR (the link

●

The BX and BLX instructions cause a Hard fault exception if bit[0] of Rm is 0.

●

The BL and BLX instructions also set bit[0] of the LR to 1. This ensures that the value is

suitable for use by a subsequent POP {PC} or BX instruction to perform a successful

return branch.

Table 22 shows the ranges for the various branch instructions.

Table 21.

Branch and control instructions

Mnemonic

Brief description

See

B{cc}

Branch {conditionally}

B, BL, BX, and BLX on page 59

Branch with link

BLX

Branch indirect with link

Branch indirect

Table 22.

Branch ranges

Instruction

Branch range

B label

−2 KB to +2 KB

Bcond label

−256 bytes to +254 bytes

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