Program

New to the Little Man Computer? Open Reference and read About the LMC. Hover the numbers in the margin to see what each machine-code word means. Click a line number (or press F9 on a line) to set a breakpoint.

Fetch–decode–execute

  1. Fetch
  2. Decode
  3. Execute

CPU and registers

Yellow: a register or unit that has just been written or is doing the work. Blue dashed outline: a register being read. The buses use the colours of the steps in Fetch–decode–execute.

Inbox

Outbox

Memory (mailboxes 00–99)

  • next
  • read
  • write

Double-click a mailbox to change its value.

Trace table
StepPCCIRInstructionACC afterMailbox changeOutput