You can find several browser based simulators for the LMC CPU online. It will dump output.Īlternatively you can copy paste this and put the code into one of the web based LMC simulators described below. You can feed this to the simulate!(program, inputs) function to run your program. You can take a program written as the example store it in a file and give that filename to the assemble(file) function which will produce a list of 3-digit integers representing your program and data. ONE DAT 1 // Store 1 in this memory address. QUIT HLT // Label this memory address as QUIT SUB ONE // Subtract from accumulator what is stored in ONEīRA LOOP // Jump (unconditionally) to the memory address labeled LOOP LOOP BRZ QUIT // Jump to QUIT if accumulator is 0 So if it reads a 4 on input, then it will write out 4, 3, 2, 1 and 0 on the output. Here is an example of a program which reads a number from the input and then counts down. In the example folder you can find more examples of programs.

OUT 902 push value in accumulator into output queue.

INP 901 fill accumulator with number from input.

BRP 8xx jump if accumulator is zero or higher (positive).

BRA 6xx jump to location xx in program.

LDA 5xx load accumulator with contents at address xx in memory.

STA 3xx store accumulator at address xx in memory.

SUB 2xx subtract contents of address xx from what is stored in the accumulator.ADD 1xx add content at address xx in memory to accumulator.

So 142 is the instruction for adding the contents of memory cell 42 to the contents of the accumulator. What this really means is that the xx are where you put your operand (argument). the Add instruction is described as having the number 1xx. Here is a tip on how to read the description below. But usually when programming one deals with letter abbreviations which are easier to remember. Each instruction is really just a 3-digit number. Here is a simple overview of the instructionset. There is also an input and ouput where you can read user input and write outputs to the user. The CPU has a single accumulator which is used when performing arithmetic. Here we can store instructions for the computer to perform or data to operate on. You can place program instructions and data here.Įach cell can hold a 3-digit decimal number. It contains 100 memory cells, numbered from 0-99. To make things simpler it is not presented as a binary computer but a decimal one. The Little Man Computer (LMC) is a very simply microprocessor and computer system designed for teaching beginners assembly programming.

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