Puzzle 87 of 100

A decoder

Goal

Make one output high for each value of A1 A0: Y0 while it is 00, Y1 while it is 01, Y2 while it is 10, and Y3 while it is 11.

Die: 34 by 26 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: A0, A1
Outputs: Y0, Y1, Y2, Y3
Supply: VDD
Ground: GND

Go to the solution

New in this puzzle

Decoding

A decoder has one output for each combination of its inputs, and exactly one output is high at a time. With every input and its inverse available, each output is a gate that reads one signal of each pair.

Hint

Each output is high for one combination only, so it is a NOR gate of the two signals that are low in that combination. The inverters of A1 and A0 are drawn: feed each NOR gate an input or its inverse from each pair.

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 87, A decoder, 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 87, A decoder, 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 87, A decoder, 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

Metal323 squares
Polysilicon104 squares
Contact78 squares
N active46 squares
P active92 squares
N well170 squares
Metal 2201 squares
Via40 squares
Input padA0, A1
Output padY0, Y1, Y2, Y3
Supply padVDD
Ground padGND
Squares you draw, change, or erase400 squares

About the drawing

The drawing uses 572 of the die's 884 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 291 empty squares and change 109 drawn squares.
It forms 20 transistors: 10 N transistors and 10 P transistors. Each one is a place where polysilicon crosses active silicon.
78 contacts join metal to the polysilicon or active silicon under it.
40 vias join metal 2 to the metal under it.

Starting drawing for puzzle 87, A decoder, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.