Puzzle 43 of 100

A two-way switch

Goal

Make Y follow A while S is low and B while S is high. SN is always the inverse of S.

Die: 15 by 13 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: SN, A, B, S
Output: Y

New in this puzzle

Two switches, one output

Two transmission gates that share an output, with their controls the other way around, form a two-way switch. Exactly one of them conducts at any moment, so the output always follows one input.

Hint

Add a second transmission gate between B and Y that conducts while S is high. SN runs along the top and S along the bottom, so draw this gate the other way up, with its P transistor on top and its N transistor below.

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 43, A two-way switch, 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 43, A two-way switch, 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 43, A two-way switch, 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

Metal33 squares
Polysilicon36 squares
Contact10 squares
N active10 squares
P active10 squares
N well30 squares
Input padSN, A, B, S
Output padY
Squares you draw, change, or erase28 squares

About the drawing

The drawing uses 86 of the die's 195 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 28 empty squares.
It forms 4 transistors: 2 N transistors and 2 P transistors. Each one is a place where polysilicon crosses active silicon.
10 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 43, A two-way switch, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.