Atmel SAM4S-XPLD Atmel ATSAM4S-XPLD ATSAM4S-XPLD Hoja De Datos

 94

SAM4S [DATASHEET]

11100E–ATARM–24-Jul-13

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 one of:

LDR

Load Register.

STR

Store Register.

type

is one of:

B

unsigned byte, zero extend to 32 bits on loads.

SB

signed byte, sign extend to 32 bits (LDR only).

H

unsigned halfword, zero extend to 32 bits on loads.

SH

signed halfword, sign extend to 32 bits (LDR only).

-

omit, for word.

cond

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 register Rn. The assembly language syntax for this mode is:

[Rn, #offset]!

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