Immediate Offset (AM 2)Immediate Offset (AM 2)[basereg, #+/-value]
where:
|
basereg |
Specifies a register containing the base address. |
|
value |
Specifies the 12-bit immediate offset used with the value of basereg to form the address. |
if U == 1 then
addr
= basereg + value
else /* U == 0 */
addr
= basereg - value
This addressing mode calculates an address by adding or subtracting the value of an immediate offset to or from the value of the base register basereg . It is used for accessing structure fields, and accessing parameters and local variables in a stack frame. If the offset is zero, the address generated is the value of the base register basereg .
|
31 |
|
|
28 |
27 |
26 |
25 |
24 |
23 |
22 |
21 |
20 |
19 |
|
|
16 |
|
condition |
0 |
1 |
0 |
1 |
U |
B |
0 |
L |
basereg |
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|
15 |
|
|
12 |
11 |
|
|
|
|
|
|
|
|
|
|
0 |
|
dest |
value |
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The B bit indicates an unsigned byte ( B == 1 ) or a word access ( B == 0 ).
The L bit indicates a Load ( L == 1 ) or a Store ( L == 0 ) instruction.
NoteThe syntax [basereg] is treated as an abbreviation for [basereg, #0] . If the instruction is one of the instructions that permit only post-indexed addressing modes ( LDRBT , LDRT , STRBT , or STRT ), the syntax [basereg] is not treated as an abbreviation for [basereg, #0] .
If R15 is specified as register basereg , the value used is the address of the current instruction plus 8.LDR R3, [R1, #0xFF]