Instruction Syntax

Mnemonic	Format	Flags
stbx	rS,rA,rB	None

Instruction Encoding

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

if rA = 0 then EA ← (rB)
else EA ← (rA) + (rB)
MEM(EA, 1) ← (rS)[24:31]

The effective address is calculated by adding the base register to the index register, or just the index register if rA is 0. 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

Related Instructions

stb, stbu, stbux, lbzx