// This file is part of the materials accompanying the book 

// "The Elements of Computing Systems" by Nisan and Schocken, 

// MIT Press. Book site: www.idc.ac.il/tecs

// File name: projects/03/2/RAM4K.hdl



/**

 * Memory of 4K registers, each 16-bit wide.  

 * The chip facilitates read and write operations, as follows:

 *     Read:  out(t) = RAM4K[address(t)](t)

 *     Write: If load(t-1) then RAM4K[address(t-1)](t) = in(t-1)

 * In words: the chip always outputs the value stored at the memory 

 * location specified by address. If load=1, the in value is loaded 

 * into the memory location specified by address.  This value becomes 

 * available through the out output starting from the next time step.

 */



CHIP RAM4K {



    IN  in[16], load, address[12];

    OUT out[16];



    PARTS:

    DMux8Way(in=load, sel=address[0..2],

             a=load0,

             b=load1,

             c=load2,

             d=load3,

             e=load4,

             f=load5,

             g=load6,

             h=load7);



     RAM512(in=in, load=load0, address=address[3..11], out=out0);

     RAM512(in=in, load=load1, address=address[3..11], out=out1);

     RAM512(in=in, load=load2, address=address[3..11], out=out2);

     RAM512(in=in, load=load3, address=address[3..11], out=out3);

     RAM512(in=in, load=load4, address=address[3..11], out=out4);

     RAM512(in=in, load=load5, address=address[3..11], out=out5);

     RAM512(in=in, load=load6, address=address[3..11], out=out6);

     RAM512(in=in, load=load7, address=address[3..11], out=out7);



     Mux8Way16(a=out0,

               b=out1,

               c=out2,

               d=out3,

               e=out4,

               f=out5,

               g=out6,

               h=out7,

               sel=address[0..2], out=out);

}