stbx
Store Byte Indexed - 7C 00 00 1C
stbx
Instruction Syntax
| Mnemonic | Format | Flags |
| stbx | rS,rA,rB | None |
Instruction Encoding
0
1
1
1
1
1
S
S
S
S
S
A
A
A
A
A
B
B
B
B
B
0
0
0
0
0
0
0
0
0
0
0
| Field | Bits | Description |
| Primary Opcode | 0-5 | 011111 (0x1F) |
| rS | 6-10 | Source register |
| rA | 11-15 | Base register |
| rB | 16-20 | Index register |
| Reserved | 21-29 | 000000000 |
| Reserved | 30-31 | 00 |
Operation
EA ← (rA) + (rB) (EA) ← (rS)[24:31]
The effective address is calculated by adding the base register to the index register. The least significant byte of the source register is stored at the effective address.
Note: The stbx instruction stores the least significant byte (bits 24-31) of the source register to memory using indexed addressing.
Affected Registers
Memory
- Byte at effective address (EA)
Examples
Basic Store Byte Indexed
# Store byte using indexed addressing stbx r3, r4, r5 # Store byte from r3 at address r4 + r5
Array Access with Index
# Store byte in array using index register li r4, array # Load array base address li r5, 2 # Index = 2 stbx r3, r4, r5 # Store byte at array[2]
Dynamic Addressing
# Store byte using dynamic index li r4, base_addr # Load base address add r5, r6, r7 # Calculate index dynamically stbx r3, r4, r5 # Store byte at base_addr + index