Datasheet
97
SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
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 90.
Table 10-18 shows the ranges of offset for immediate, pre-indexed and post-indexed forms.
10.12.2.6 Restrictions
For load instructions:
Rt can be SP or PC for word loads only
Rt must be different from Rt2 for two-word loads
Rn must be different from Rt and Rt2 in the pre-indexed or post-indexed forms.
When Rt is PC in a word load instruction:
bit[0] of the loaded value must be 1 for correct execution
a branch occurs to the address created by changing bit[0] of the loaded value to 0
if the instruction is conditional, it must be the last instruction in the IT block.
For store instructions:
Rt can be SP for word stores only
Rt must not be PC
Rn must not be PC
Rn must be different from Rt and Rt2 in the pre-indexed or post-indexed forms.
10.12.2.7 Condition flags
These instructions do not change the flags.
10.12.2.8 Examples
LDR R8, [R10] ; Loads R8 from the address in R10.
LDRNE R2, [R5, #960]! ; Loads (conditionally) R2 from a word
; 960 bytes above the address in R5, and
; increments R5 by 960.
STR R2, [R9,#const-struc] ; const-struc is an expression evaluating
; to a constant in the range 0-4095.
STRH R3, [R4], #4 ; Store R3 as halfword data into address in
; R4, then increment R4 by 4
LDRD R8, R9, [R3, #0x20] ; Load R8 from a word 32 bytes above the
; address in R3, and load R9 from a word 36
; bytes above the address in R3
STRD R0, R1, [R8], #-16 ; Store R0 to address in R8, and store R1 to
; a word 4 bytes above the address in R8,
; and then decrement R8 by 16.
Table 10-18. Offset ranges
Instruction type Immediate offset Pre-indexed Post-indexed
Word, halfword, signed halfword,
byte, or signed byte
−255 to 4095 −255 to 255 −255 to 255
Two words
multiple of 4 in the range
−1020 to 1020
multiple of 4 in the range
−1020 to 1020
multiple of 4 in the range
−1020 to 1020