beautiful-racket/beautiful-racket-demo/hdl/Dmux4Way.hdl.rkt

#lang br/demo/hdl

// This file is part of www.nand2tetris.org
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/01/DMux4Way.hdl

/**
 * 4-way demultiplexor:
 * {a, b, c, d} = {in, 0, 0, 0} if sel == 00
 *                {0, in, 0, 0} if sel == 01
 *                {0, 0, in, 0} if sel == 10
 *                {0, 0, 0, in} if sel == 11
 */

CHIP DMux4Way {
    // todo: how should sel subscripting work?
    IN in, sel[2];
    OUT a, b, c, d;

    PARTS:
    DMux(in=in, sel=sel[0], a=a, b=b);
    DMux(in=in, sel=sel[1], a=c, b=d);
    /*
    // the right answer: note that subscripting on right always means "read this bit";
    // subscripting on left means "write this bit"
    // build out assignment operator
    DMux(in=in, sel=sel[0], a=s0a, b=s0b);
    DMux(in=s0b, sel=sel[1], a=b, b=d);
    DMux(in=s0a, sel=sel[1], a=a, b=c);
    */
}