80 lines
2.0 KiB
Plaintext
80 lines
2.0 KiB
Plaintext
// This file is part of www.nand2tetris.org
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// and the book "The Elements of Computing Systems"
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// by Nisan and Schocken, MIT Press.
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// File name: projects/03/a/PC.hdl
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/**
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* A 16-bit counter with load and reset control bits.
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* if (reset[t] == 1) out[t+1] = 0
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* else if (load[t] == 1) out[t+1] = in[t]
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* else if (inc[t] == 1) out[t+1] = out[t] + 1 (integer addition)
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* else out[t+1] = out[t]
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*/
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CHIP PC {
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IN in[16],load,inc,reset;
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OUT out[16];
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PARTS:
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// We use this IF inc=1
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Inc16(in=registerout, out=incrementedoutput);
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// We setup a Mux using the 3 bits as the inputs
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// for the Mux. Higher priority uses MSB
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// [ reset | load | inc ]
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// [ sel[2]|sel[1]|sel[0] ]
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// DO NOTHING For this case
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// a if sel == 000
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// INC for this case
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// b if sel == 001
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// LOAD for the below 2 cases
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// c if sel == 010
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// d if sel == 011
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// RESET for all 4 cases below
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// e if sel == 100
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// f if sel == 101
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// g if sel == 110
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// h if sel == 111
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// a-d: we reset
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// e-f: we load
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// g: we increment
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// h: do nothing
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// We don't have a Or3Way, so using this for now
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// This sets pleaseupdate to true if either of the
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// reset|load|inc operations is in call
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Or8Way(
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in[0]=inc,
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in[1]=load,
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in[2]=reset,
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in[3]=false,
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in[4]=false,
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in[5]=false,
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in[6]=false,
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in[7]=false,
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out=pleaseupdate);
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Mux8Way16(
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// While this is false it doesn't matter
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// since pleaseupdate = 0 in this case
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// and register won't reset
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a=false,
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// INCREMENT for this case
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b=incrementedoutput,
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// LOAD for these 2 cases
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c=in,
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d=in,
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// please pass 0 as input to the register
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// RESET
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e=false,
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f=false,
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g=false,
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h=false,
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sel[2]=reset,
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sel[1]=load,
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sel[0]=inc,
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out=registerinput);
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Register(in=registerinput, load=pleaseupdate, out=registerout, out=out);
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}
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