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// This file is part of
// and the book "The Elements of Computing Systems"
// by Nisan and Schocken, MIT Press.
// File name: projects/05/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. 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 book.
CHIP Memory {
IN in[16], load, address[15];
OUT out[16];
DMux(in=load, sel=address[14], a=ramload, b=ioload); // 1 {
DMux(in=ioload, sel=address[13], a=scrload, b=kbload); // 2 {
RAM16K(in=in, load=ramload, address=address[0..13], out=ramout);
Screen(in=in, load=scrload, address=address[0..12], out=scrout);
Mux16(a=scrout, b=kbout, sel=address[13], out=ioout); // } 2
Mux16(a=ramout, b=ioout, sel=address[14], out=out); // } 1