Projects, 01-06 completed

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+// 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/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];

+

+    PARTS:

+    // RAM16K

+    Not(in=address[14], out=notaddr14);

+    And(a=notaddr14, b=load, out=loadRAM16K);

+    RAM16K(in=in, load=loadRAM16K, address=address[0..13], out=outRAM16K);

+    // Screen

+    Not(in=address[13], out=notaddr13);

+    And(a=notaddr13, b=address[14], out=screenaddr);

+    And(a=screenaddr, b=load, out=loadScreen);

+    Screen(in=in, load=loadScreen, address=address[0..12], out=outScreen);

+    // Keyboard

+    Keyboard(out=outKeyboard);

+    Mux16(a=outScreen, b=outKeyboard, sel=address[13], out=scrkbd);

+    Mux16(a=outRAM16K, b=scrkbd, sel=address[14], out=out);

+}