PM0214 datasheet(70/245 Pages) STMICROELECTRONICS

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The STM32 Cortex-M4 instruction set

PM0214

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DocID022708 Rev 4

3.4.2

LDR and STR, immediate offset

Load and store with immediate offset, pre-indexed immediate offset, or post-indexed

immediate offset.

Syntax

op{type}{cond} Rt, [Rn {, #offset}]; immediate offset

op{type}{cond} Rt, [Rn, #offset]!; pre-indexed

op{type}{cond} Rt, [Rn], #offset; post-indexed

opD{cond} Rt, Rt2, [Rn {, #offset}]; immediate offset, two words

opD{cond} Rt, Rt2, [Rn, #offset]!; pre-indexed, two words

opD{cond} Rt, Rt2, [Rn], #offset; post-indexed, two words

where:

•

‘op’ is either LDR (load register) or STR (store register)

•

‘type’ is one of the following:

B: Unsigned byte, zero extends to 32 bits on loads

SB: Signed byte, sign extends to 32 bits (LDR only)

H: Unsigned halfword, zero extends to 32 bits on loads

SH: Signed halfword, sign extends to 32 bits (LDR only)

—: Omit, for word

•

‘cond’ is an optional condition code (see Conditional execution on page 64)

•

‘Rt’ is the register to load or store

•

‘Rn’ is the register on which the memory address is based

•

‘offset’ is an offset from Rn. If offset is omitted, the address is the contents of Rn

•

‘Rt2’ is the additional register to load or store for two-word operations

Operation

LDR instructions load one or two registers with a value from memory. STR instructions store

one or two register values to memory.

Load and store instructions with immediate offset can use the following addressing modes:

•

Offset addressing

The offset value is added to or subtracted from the address obtained from the register

Rn. The result is used as the address for the memory access. The register Rn is

unaltered. The assembly language syntax for this mode is: [Rn, #offset].

•

Pre-indexed addressing

The offset value is added to or subtracted from the address obtained from the register

Rn. The result is used as the address for the memory access and written back into the

•

Post-indexed addressing

The address obtained from the register Rn is used as the address for the memory

access. The offset value is added to or subtracted from the address, and written back

into the register Rn. The assembly language syntax for this mode is: [Rn], #offset.

The value to load or store can be a byte, halfword, word, or two words. Bytes and halfwords

can either be signed or unsigned (see Address alignment on page 64).

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