Tools

Little Man Computer (LMC) Simulator

Write LMC assembly programs, assemble them and step through execution one instruction at a time. Watch the accumulator, program counter and all 100 mailboxes update in real time. Used by OCR GCSE and various A Level courses to teach low-level programming concepts.

LMC Assembly // for comments  ·  LABEL before instruction
Accumulator
000
Program Counter
00
Output

Output will appear here when OUT is executed

Memory (100 mailboxes)
0
000
1
000
2
000
3
000
4
000
5
000
6
000
7
000
8
000
9
000
10
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11
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22
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24
000
25
000
26
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27
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28
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29
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30
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31
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32
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33
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34
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35
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36
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37
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38
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39
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40
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42
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99
000
Instruction set
INP Input → ACC
OUT ACC → Output
HLT Stop
ADD xx ACC + mem[xx]
SUB xx ACC − mem[xx]
STA xx ACC → mem[xx]
LDA xx mem[xx] → ACC
BRA xx Jump to xx
BRZ xx Jump if ACC=0
BRP xx Jump if ACC≥0
DAT n Define data n