Puzzle 82 of 100

Three-input exclusive OR

Goal

Make Y high while an odd number of A, B, and C are high: one of them, or all three. The exclusive OR of A and B is drawn.

Die: 34 by 22 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: A, B, C
Output: Y
Supply: VDD
Ground: GND

Go to the solution

New in this puzzle

An odd count

A three-input exclusive OR is high while an odd number of its inputs are high. Two exclusive OR gates in a chain compute it, and it is the sum bit of a full adder.

Hint

Y is the exclusive OR of the drawn output and C. One way to build it is a NOR gate of the two signals feeding a compound gate that pulls Y low while both signals are high or while their NOR is high.

Solution

This is the game's reference drawing for the puzzle. It meets the goal and passes the design rules. Other drawings can pass as well.

Top View of the solved die for puzzle 82, Three-input exclusive OR, with the Side View below it. — Top View of the solved die, captured from the game. Paths that carry a high level at the moment shown are lit. The Side View below cuts through the row between the dashed lines.

The game window in Isometric View with the solved die for puzzle 82, Three-input exclusive OR, the guide, and the scope. — The whole game window in Isometric View. The scope on the right compares each output with its target band, and the message above it confirms that the drawing passes.

Solution drawing for puzzle 82, Three-input exclusive OR, drawn on a numbered grid with every layer in its game color and pattern. — The solution on the grid. Squares are numbered from the top left corner, so you can count them. The dashed outline marks the squares you draw, change, or erase; the rest is drawn when the puzzle opens.

Legend

Metal243 squares
Polysilicon98 squares
Contact68 squares
N active46 squares
P active84 squares
N well170 squares
Metal 2210 squares
Via39 squares
Input padA, B, C
Output padY
Supply padVDD
Ground padGND
Squares you draw, change, or erase197 squares

About the drawing

The drawing uses 499 of the die's 748 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 130 empty squares and change 67 drawn squares.
It forms 20 transistors: 10 N transistors and 10 P transistors. Each one is a place where polysilicon crosses active silicon.
68 contacts join metal to the polysilicon or active silicon under it.
39 vias join metal 2 to the metal under it.

Starting drawing for puzzle 82, Three-input exclusive OR, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.