感想

Nand2tetris是以實作project來讓學生更加認識電腦底層，project會設計到數位邏輯、設計簡單的cpu、組合語言、指令集、虛擬機，目前本人才開始做第一章，是利用HDL設計邏輯閘，且只限定使用Nand來實作，當中複習了笛摩根定理、真值表…等觀念，以下為我目前的實作

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AND閘 
Nand自己做反相器

CHIP And {
    IN a, b;
    OUT out;
    
    PARTS:
    //// Replace this comment with your code.
    
    Nand(a=a,b=b,out=neq1);
    Nand(a= neq1 , b = neq1,out=out);

}
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多工器  

* if (sel == 0) out = a, else out = b

a AND Not(sel) | b And sel

CHIP Mux {
    IN a, b, sel;
    OUT out;

    PARTS:
    //// Replace this comment with your code.
    Nand(a=sel , b=sel , out = Notsel);
    Nand(a=a , b= Notsel , out = AandSel) ; 
    Nand(a = AandSel , b = AandSel , out = outA) ; 

    Nand(a=b , b= sel , out = BandSel) ; 
    Nand(a = BandSel , b = BandSel , out = outB) ; 

    Nand(a=outA , b = outA , out = A);
    Nand(a=outB , b = outB , out = B);

    Nand(a = A , b = B ,out = out);


    

}
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解多工器，兩條輸出選擇其中一條

類似想法: 
子網路遮罩通過255.255.255.255，所有位元數都為1，對遮罩進行AND運算並不會改變原本的IP
我們需要留下input，所以如果有值，in需要和1做AND才得以保留


* Demultiplexor:
 * [a, b] = [in, 0] if sel == 0
 *          [0, in] if sel == 1
 *
CHIP DMux {
    IN in, sel;
    OUT a, b;

    PARTS:
    //// Replace this comment with your code.
    Nand(a= sel , b = sel , out = notSel) ; 

    Nand(a = notSel , b = in  , out = enq1) ; 
    Nand(a = enq1 , b = enq1 , out = a) ; 

    Nand(a= sel , b = in , out = enq2) ; 
    Nand(a = enq2 , b = enq2 , out = b) ; 
}

解多工器真值表

in , sel a , b
0 0 in 0
1 0 in 0
0 1 0 in
1 1 0 in

其他是將上述邏輯閘擴展位元，將在其他篇章介紹