Puzzle 38 of 100

An extra square

Goal

Y should be low while A or B is high and C is also high. One square joins two nets that should be apart: find it and remove it.

Die: 13 by 15 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: A, B, C
Output: Y
Supply: VDD
Ground: GND

Go to the solution

New in this puzzle

Outlining a net

Pointing at a conducting square outlines every square joined to it. A net that reaches further than it should leads to the place where two nets touch.

Hint

Compare Y with its target: Y falls whenever C is high, as if A and B did not matter. Point at the metal over the N strip to outline its net, and look for the place where it reaches a net it should not.

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 38, An extra square, 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 38, An extra square, 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 38, An extra square, 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

Metal66 squares
Polysilicon39 squares
Contact13 squares
N active7 squares
P active14 squares
N well44 squares
Input padA, B, C
Output padY
Supply padVDD
Ground padGND
Squares you draw, change, or erase1 square

About the drawing

The drawing uses 117 of the die's 195 squares.
Part of the drawing is in place when the puzzle opens. To finish it, erase 1 square.
At column 8, row 12, erase metal.
It forms 6 transistors: 3 N transistors and 3 P transistors. Each one is a place where polysilicon crosses active silicon.
13 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 38, An extra square, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.