signal-multiplexer

              | JMP MAIN        | JMP MAIN          | JMP MAIN
              | SEND:           | L: MOV 1, DOWN    | SEND:
              | MOV UP, NIL     | MAIN:             | MOV UP, NIL
              | MAIN:           | MOV UP, ACC       | MAIN:
              | MOV RIGHT, ACC  | MOV ACC, LEFT     | MOV LEFT, ACC
              | JGZ SEND        | MOV ACC, RIGHT    | JLZ SEND
              | MOV UP, DOWN    | JEZ L             | MOV UP, DOWN
              |                 | MOV 0, DOWN       |
______________|_________________|___________________|_______________
              | MOV UP, RIGHT   | JMP MAIN          | MOV UP, LEFT
              |                 | L:                |
              |                 | MOV NIL, ACC      |
              |                 | ADD ANY           |
              |                 | MOV ACC, DOWN     |
______________|_________________|___________________|_______________
COMMUNICATION |                 | MOV UP, DOWN      |
FAILURE       |                 |                   |