// 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/RAM16K.hdl



/**

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

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

 *     Read:  out(t) = RAM16K[address(t)](t)

 *     Write: If load(t-1) then RAM16K[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 RAM16K {



    IN  in[16], load, address[14];

    OUT out[16];



    PARTS:

    DMux4Way(in=load, sel=address[0..1],

             a=load0,

             b=load1,

             c=load2,

             d=load3);



    RAM4K(in=in, load=load0, address=address[2..13], out=out0);

    RAM4K(in=in, load=load1, address=address[2..13], out=out1);

    RAM4K(in=in, load=load2, address=address[2..13], out=out2);

    RAM4K(in=in, load=load3, address=address[2..13], out=out3);



    Mux4Way16(a=out0,

              b=out1,

              c=out2,

              d=out3,

              sel=address[0..1], out=out);

}