Add solutions for part 1

projects/05/Memory.hdl

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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:
+
+    DMux4Way(in=true, sel=address[13..14], a=selectrama, b=selectramb, c=selectscreen, d=selectkeyboard);
+
+    Or(a=selectrama, b=selectramb, out=selectram);
+    And(a=load, b=selectram, out=loadram);
+    And(a=load, b=selectscreen, out=loadscreen);
+
+    RAM16K(in=in, load=loadram, address=address[0..13], out=outram);
+    Screen(in=in, load=loadscreen, address=address[0..12], out=outscreen);
+    Keyboard(out=outkeyboard);
+
+    Mux4Way16(a=outram, b=outram, c=outscreen, d=outkeyboard, sel=address[13..14], out=out);
+}