Assembly Instruction Visualiser

8086 subset. Assemble, simulate, and understand what each instruction does to registers, flags, and memory.

Program

8086 assembly

Supported mnemonics: MOV reg, imm16, ADD|SUB reg, imm16, INC|DEC reg, CMP reg, imm16, JMP label, JZ label, JNZ label, NOP, HLT. Registers: AX, BX, CX, DX, SI, DI, BP, SP. Labels end with a colon.

Assembled output

Listing

Addr	Bytes	Instruction

Hex dump

Run controls

Step executes the current instruction at IP. Run executes up to a limit or until HLT.

CPU state

FLAGS

How it works

This is a small 8086 style assembler and simulator. It assembles a limited set of mnemonics into real Intel opcodes, then executes them step by step while updating registers and common flags.

Assembler supports labels and relative jumps. It shows an address, the bytes, and the source line.
Simulator tracks registers AX, BX, CX, DX, SI, DI, BP, SP, the IP, and flags ZF, CF, SF.
Jumps use near relative addressing where possible. If a displacement exceeds 8 bit range it falls back to near 16 bit.

This is deliberately small for clarity. It is useful for learning and quick checks. It is not a full emulator.

Examples

Add two numbers

MOV AX, 1
ADD AX, 2
HLT

Count down with a loop

MOV CX, 5
loop:
DEC CX
JNZ loop
HLT

Related tools

What you are seeing

Each instruction has an opcode and operands. The assembler converts your mnemonics into bytes. The simulator then executes those bytes, updating registers and flags. This helps you see how simple arithmetic and loops work at the lowest level.

Supported opcodes

MOV r16, imm16 uses B8+rw followed by the immediate.
ADD r16, imm16 uses 05 for AX or 81 /0 for other registers.
SUB r16, imm16 uses 2D for AX or 81 /5 for other registers.
INC|DEC r16 uses 40+rw and 48+rw.
CMP r16, imm16 uses 3D for AX or 81 /7 for others.
JMP rel uses E9 near relative.
JZ/JNZ use short jumps 74/75 where possible, else near relative 0F 84/0F 85.
NOP 90, HLT F4.

This subset keeps the visuals clean while remaining faithful to 8086 behaviour for these instructions.