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diff --git a/tools/builtInChips/Screen.hdl b/tools/builtInChips/Screen.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: tools/builtIn/Screen.hdl
+
+/**
+ * The Screen (memory map).
+ * Functions exactly like a 16-bit 8K RAM:
+ *    1. out(t)=Screen[address(t)](t)
+ *    2. If load(t-1) then Screen[address(t-1)](t)=in(t-1)
+ *
+ * The built-in chip implementation has the side effect of continuously 
+ * refreshing a visual 256 by 512 black-and-white screen, simulated 
+ * by the simulator. Each row in the visual screen is represented 
+ * by 32 consecutive 16-bit words, starting at the top left corner 
+ * of the visual screen. Thus the pixel at row r from the top and 
+ * column c from the left (0<=r<=255, 0<=c<=511) reflects the c%16 
+ * bit (counting from LSB to MSB) of the word found in 
+ * Screen[r*32+c/16]. 
+ */
+
+CHIP Screen {
+
+    IN  in[16],    // what to write
+    load,          // write-enable bit
+    address[13];   // where to read/write
+    OUT out[16];   // Screen value at the given address
+
+    BUILTIN Screen;
+    CLOCKED in, load;
+}
+
+
+
+ 
+\ No newline at end of file