stb

Store Byte

stb RS, D(RA)

Stores the low 8 bits of a register to memory.

Encoding

Binary Layout

10

DS

RS

RA

SIMM[15:0]

 

Format D-form

Opcode 0x98000000

Extension Base

Operands

• RS
  Source Register
• D
  Displacement
• RA
  Base Register
• EA
  Effective Address

Example

stb r3, 0(r4)

// Store byte from r3 to address r4.

Related

More in Base

Reference

View in PowerISA v3.1C Specification ↗ OPF Power ISA v3.1C

Description

Store the low 8 bits of RS to the byte in memory at the effective address formed by adding the displacement D (sign-extended) to RA, or to the displacement alone if RA is 0. This is a Base category instruction with no status field updates.

Operation

EA ← EXTS(D, 16) + (RA | 0)
MEM(EA, 1) ← RS[56:63]

Programming Note

The stb instruction is commonly used to store a single byte from a register into memory. Ensure that the destination address is properly aligned for optimal performance and avoid accessing invalid or protected memory regions to prevent exceptions.