Atmel SAM4S Series, Preliminary Data Sheet

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11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
The memory address to load from or store to is at an offset from the register Rn. The offset is
specified by the register Rm and can be shifted left by up to 3 bits using LSL.
The value to load or store can be a byte, halfword, or word. For load instructions, bytes and half-
words can either be signed or unsigned. See
“Address Alignment” .
Restrictions
In these instructions:
• Rn must not be PC
• Rm must not be SP and must not be PC
• Rt can be SP only for word loads and word stores
• Rt can be PC only for word loads.
When Rt is PC in a word load instruction:
• Bit[0] of the loaded value must be 1 for correct execution, and a branch occurs to this
halfword-aligned address
• If the instruction is conditional, it must be the last instruction in the IT block.
Condition Flags
These instructions do not change the flags.
Examples
STR R0, [R5, R1] ; Store value of R0 into an address equal to
; sum of R5 and R1
LDRSB R0, [R5, R1, LSL #1] ; Read byte value from an address equal to
; sum of R5 and two times R1, sign extended it
; to a word value and put it in R0
STR R0, [R1, R2, LSL #2] ; Stores R0 to an address equal to sum of R1
; and four times R2
11.6.4.4 LDR and STR, unprivileged
Load and Store with unprivileged access.
Syntax
op{type}T{cond} Rt, [Rn {, #offset}] ; immediate offset
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.