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第4章 算術邏輯移位單元

簡介

「算術邏輯單元」(ALU, Arithmetic Logic Unit)

通過多工器與解多工器與記憶體位置，通過此來分配。

Nand2Tetris ALU

簡易多工器，以串級方式將多種功能拼接起來，有 zy、nx、zy、ny、f、no六種控制線，以及zr、ng比較輸出線，資料輸入是16位元的x、y，資料輸出out，簡單但相當直覺，不過多層的串級速度會有點慢。

真值表
真值表 | x | y | zx | nx | zy | ny | f | no | out | zr | ng | | ---------------- | ---------------- | --- | --- | --- | --- | --- | --- | ---------------- | --- | --- | | 0000000000000000 | 1111111111111111 | 1 | 0 | 1 | 0 | 1 | 0 | 0000000000000000 | 1 | 0 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 1 | 1 | 1 | 1 | 0000000000000001 | 0 | 0 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 1 | 0 | 1 | 0 | 1111111111111111 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 1 | 1 | 0 | 0 | 0000000000000000 | 1 | 0 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 0 | 0 | 0 | 0 | 1111111111111111 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 1 | 1 | 0 | 1 | 1111111111111111 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 0 | 0 | 0 | 1 | 0000000000000000 | 1 | 0 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 1 | 1 | 1 | 1 | 0000000000000000 | 1 | 0 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 0 | 0 | 1 | 1 | 0000000000000001 | 0 | 0 | | 0000000000000000 | 1111111111111111 | 0 | 1 | 1 | 1 | 1 | 1 | 0000000000000001 | 0 | 0 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 0 | 1 | 1 | 1 | 0000000000000000 | 1 | 0 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 1 | 1 | 1 | 0 | 1111111111111111 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 1 | 1 | 0 | 0 | 1 | 0 | 1111111111111110 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 0 | 0 | 1 | 0 | 1111111111111111 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 0 | 1 | 0 | 0 | 1 | 1 | 0000000000000001 | 0 | 0 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 0 | 1 | 1 | 1 | 1111111111111111 | 0 | 1 | | 0000000000000000 | 1111111111111111 | 0 | 0 | 0 | 0 | 0 | 0 | 0000000000000000 | 1 | 0 | | 0000000000000000 | 1111111111111111 | 0 | 1 | 0 | 1 | 0 | 1 | 1111111111111111 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 1 | 0 | 1 | 0 | 1 | 0 | 0000000000000000 | 1 | 0 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 1 | 1 | 1 | 1 | 0000000000000001 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 1 | 0 | 1 | 0 | 1111111111111111 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 1 | 1 | 0 | 0 | 0000000000010001 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 0 | 0 | 0 | 0 | 0000000000000011 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 1 | 1 | 0 | 1 | 1111111111101110 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 0 | 0 | 0 | 1 | 1111111111111100 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 1 | 1 | 1 | 1 | 1111111111101111 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 0 | 0 | 1 | 1 | 1111111111111101 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 0 | 1 | 1 | 1 | 1 | 1 | 0000000000010010 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 0 | 1 | 1 | 1 | 0000000000000100 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 1 | 1 | 1 | 0 | 0000000000010000 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 1 | 1 | 0 | 0 | 1 | 0 | 0000000000000010 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 0 | 0 | 1 | 0 | 0000000000010100 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 0 | 1 | 0 | 0 | 1 | 1 | 0000000000001110 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 0 | 1 | 1 | 1 | 1111111111110010 | 0 | 1 | | 0000000000010001 | 0000000000000011 | 0 | 0 | 0 | 0 | 0 | 0 | 0000000000000001 | 0 | 0 | | 0000000000010001 | 0000000000000011 | 0 | 1 | 0 | 1 | 0 | 1 | 0000000000010011 | 0 | 0 |
Verilog程式碼
Verilog測試檔案
HDL 程式碼 
// 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/02/ALU.hdl

/**
 * The ALU (Arithmetic Logic Unit).
 * Computes one of the following functions:
 * x+y, x-y, y-x, 0, 1, -1, x, y, -x, -y, !x, !y,
 * x+1, y+1, x-1, y-1, x&y, x|y on two 16-bit inputs,
 * according to 6 input bits denoted zx,nx,zy,ny,f,no.
 * In addition, the ALU computes two 1-bit outputs:
 * if the ALU output == 0, zr is set to 1; otherwise zr is set to 0;
 * if the ALU output < 0, ng is set to 1; otherwise ng is set to 0.
 */

// Implementation: the ALU logic manipulates the x and y inputs
// and operates on the resulting values, as follows:
// if (zx == 1) set x = 0        // 16-bit constant
// if (nx == 1) set x = !x       // bitwise not
// if (zy == 1) set y = 0        // 16-bit constant
// if (ny == 1) set y = !y       // bitwise not
// if (f == 1)  set out = x + y  // integer 2's complement addition
// if (f == 0)  set out = x & y  // bitwise and
// if (no == 1) set out = !out   // bitwise not
// if (out == 0) set zr = 1
// if (out < 0) set ng = 1

CHIP ALU {
    IN
        x[16], y[16],  // 16-bit inputs
        zx, // zero the x input?
        nx, // negate the x input?
        zy, // zero the y input?
        ny, // negate the y input?
        f,  // compute out = x + y (if 1) or x & y (if 0)
        no; // negate the out output?

    OUT
        out[16], // 16-bit output
        zr, // 1 if (out == 0), 0 otherwise
        ng; // 1 if (out < 0),  0 otherwise

    PARTS:
    Mux16(a=x, b[0..15]=false, sel=zx, out=xMuxZero);

    Not16(in=xMuxZero, out=xBar);
    Mux16(a=xMuxZero, b=xBar, sel=nx, out=xMuxxBar);

    Mux16(a=y, b[0..15]=false, sel=zy, out=yMuxZero);

    Not16(in=yMuxZero, out=yBar);
    Mux16(a=yMuxZero, b=yBar, sel=ny, out=yMuxyBar);

    And16(a=xMuxxBar, b=yMuxyBar, out=XAndY);
    Add16(a=xMuxxBar, b=yMuxyBar, out=XAddY);
    Mux16(a=XAndY, b=XAddY, sel=f, out=AndMuxOr);

    Not16(in=AndMuxOr, out=AndMuxOrBar);
    Mux16(a=AndMuxOr, b=AndMuxOrBar, sel=no, out=out, out[0..7]=or8way1, out[8..15]=or8way2, out[15]=and);

    Or8Way(in=or8way1, out=zr1);
    Or8Way(in=or8way2, out=zr2);
    Or(a=zr1, b=zr2, out=zr3);
    Not(in=zr3, out=zr);
    And(a=and, b=true, out=ng);
}