16 bit Assembly
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MOVSB and MOVSW - Move Far Instruction
The MOVSB and MOVSW instructions are used to move data between segments from the address pointed to by the DS:SI register to the address of the ES:DI Register.
After each call the SI and DI Registers are incremented by one byte for byte operations or by two bytes for WORD.
This command has 1 part, the Instruction.
SI and DI are decremented backwards when the direction flag is set using the STD instruction.
MOVSB moves one byte at a time. Op Code A4. MOVSW moves 2 bytes at a time. Op Code A5
Unlike LODSB and LODSW it can be used to move data between sements.
This example moves 16 single bytes before exiting the LOOP.
| Assembly Sample | Description | 16 bit Machine Code |
|---|---|---|
| MOV CX, 0x0010 | ; Assign 10h (16) to the Counter CX | B9 10 00 |
| MOV SI, DataString | ; Assign SI to point at a memory location to be read. | BE 26 01 |
| MOV DI, DataOut | ; Assign DI to point at a memory location to save in. | BF 36 01 |
| MOVSB | ; Load one byte into AL | A4 |
| LOOP 0xFD | ; LOOP back to LODSB to read each byte until CX = 0 | E2 FD |
Last Update 06/02/2023