stw
Store Word - 90 00 00 00
stw
Instruction Syntax
| Mnemonic | Format | Flags |
| stw | rS,d(rA) | None |
Instruction Encoding
1
0
0
1
0
0
S
S
S
S
S
A
A
A
A
A
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
| Field | Bits | Description |
| Primary Opcode | 0-5 | 100100 (0x24) |
| rS | 6-10 | Source register |
| rA | 11-15 | Base register |
| SIMM | 16-31 | Signed immediate offset |
Operation
EA ← (rA) + SIMM (EA) ← (rS)
The effective address is calculated by adding the signed immediate offset to the base register. The word (32-bit value) in the source register is stored at the effective address.
Note: The stw instruction stores a 32-bit word to memory. The address must be aligned to a 4-byte boundary.
Affected Registers
Memory
- Word at effective address (EA)
Examples
Basic Store Word
# Store word from r1 to memory stw r1, 0(r3) # Store at address in r3 stw r1, 4(r3) # Store at address r3 + 4
Array of Words
# Store word in array li r4, 0 # Array index slwi r4, r4, 2 # Multiply by 4 (word size) add r5, r3, r4 # Calculate address stw r1, 0(r5) # Store word
Data Structure Access
# Store word in data structure li r3, struct_base # Load structure base address li r4, 8 # Offset to field stw r1, 8(r3) # Store word at struct.field