Samsung S3C2440A User Manual
Page 91
ARM INSTRUCTION SET
S3C2440A RISC MICROPROCESSOR
3-34
HALFWORD AND SIGNED DATA TRANSFER (LDRH/STRH/LDRSB/LDRSH)
The instruction is only executed if the condition is true. The various conditions are defined in Table 3-2. The
instruction encoding is shown in Figure 3-16.
These instructions are used to load or store half-words of data and also load sign-extended bytes or half-words of
data. The memory address used in the transfer is calculated by adding an offset to or subtracting an offset from a
base register. The result of this calculation may be written back into the base register if auto-indexing is required.
31
27
19
15
Cond
28
16
11
12
21
23
0
20
L
Rn
Rd
[3:0] Offset Register
[6][5] S H
0 0 = SWP instruction
0 1 = Unsigned halfword
1 1 = Signed byte
1 1 = Signed halfword
[15:12] Source/Destination Register
[19:16] Base Register
[20] Load/Store
0 = Store to memory
1 = Load from memory
[21] Write-back
0 = No write-back
1 = Write address into base
[23] Up/Down
0 = Down: subtract offset from base
1 = Up: add offset to base
[24] Pre/Post Indexing
0 = Post: add/subtract offset after transfer
1 = Pre: add/subtract offset bofore transfer
[31:28] Condition Field
22
000
P U
0000
W
24
25
1
Rm
S H 1
8 7 6
5 4 3
0
Figure 3-16. Halfword and Signed Data Transfer with Register Offset