The Little Man Computer

The Little Man Computer is a simplified computer that works on Von Neuman principles. It has all the CPU components we have detailed above. It is programmed in machine code but for simplicity it uses the denary rather than the binary number system.

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On the left is the instruction set. Each number constitutes and execution routine and the xx stand for the address in RAM that the execution will work on.

Each row of the RAM has a denary address, 1 through to 99. Each address can hold three digits.

  • So the instruction 560 would mean load the number at address 60.
  • The instruction 340 would mean store a datum at address 40

Working through a basic computation

We are going to add two numbers together as a basic example.

  1. First we need to place the two numbers in RAM we are going to use 5 and 3
    • At address 60 we will put the number 5 and at address 61 we will put the number 3
    • We are going to start at address 0 in the top left of the RAM grid
  2. The first instruction will be load address 60 which in the assembly will be 560 . We put this in address 0, our starting point.
  3. This first instruction is now stored in the accumulator.
  4. Now we want to add this number (in the accumulator) to the number in address 61
  5. This second instruction is 161 . We write this in address 1
  6. Finally we want to store the output of the calculation in the RAM, let’s say at address 62
  7. So we store the command 362 at address 2
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