Memory.hdl

// 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/5/Memory.hdl
/**
 * The complete address space of the Hack computer's memory,
 * including RAM and memory-mapped I/O. 
 * The chip facilitates read and write operations, as follows:
 *     Read:  out(t) = Memory[address(t)](t)
 *     Write: if load(t-1) then Memory[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 from the next time step onward.
 * Address space rules:
 * Only the upper 16K+8K+1 words of the Memory chip are used. 
 * Access to address>0x6000 is invalid and reads 0. Access to any address
 * in the range 0x4000-0x5FFF results in accessing the screen memory 
 * map. Access to address 0x6000 results in accessing the keyboard 
 * memory map. The behavior in these addresses is described in the Screen
 * and Keyboard chip specifications given in the lectures and the book.
 */
CHIP Memory {
    IN in[16], load, address[15];
    OUT out[16];

    PARTS:
	//// Replace this comment with your code.
    Not(in=address[14],out=memo);
    And(a=load,b=memo,out=load1);
    RAM16K(in=in,load=load1,address=address[0..13],out=out1);

    Not(in=address[13],out=scrn);
    And(a=address[14],b=scrn,out=one);
    And(a=load,b=one,out=load2);
    Screen(in=in,load=load2,address=address[0..12],out=out2);

    Keyboard(out=out3);

    Not(in=address[13],out=notkey);
    And(a=notkey,b=address[14],out=slt);
    Mux16(a=out1,b=out2,sel=slt,out=out4);
    And(a=address[14],b=address[13],out=select);
    Mux16(a=out4,b=out3,sel=select,out=out);
}