Puzzle 98 of 100

Count to three and stop

Goal

Make Q1 and Q0 count 0, 1, 2, 3 on rising edges of CLK and then stay at 3.

Die: 35 by 29 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: CLK, CLKN
Outputs: Q0, Q1
Supply: VDD, VDD
Ground: GND, GND

Go to the solution

New in this puzzle

A state that holds

Next state logic can lead a state back to itself. Once the machine reaches such a state it stays there, as a counter that stops at its last value.

Hint

Q1 goes high once either bit is high, so D1 is a NAND gate of QN1 and QN0. Q0 goes low only from the count 1, so D0 is a NAND gate of Q0 and QN1.

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 98, Count to three and stop, 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 98, Count to three and stop, 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 98, Count to three and stop, 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

Metal295 squares
Polysilicon88 squares
Contact54 squares
N active32 squares
P active32 squares
N well132 squares
Metal 2349 squares
Via63 squares
Input padCLK, CLKN
Output padQ0, Q1
Supply padVDD, VDD
Ground padGND, GND
Squares you draw, change, or erase222 squares

About the drawing

The drawing uses 633 of the die's 1015 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 205 empty squares and change 17 drawn squares.
It forms 24 transistors: 12 N transistors and 12 P transistors. Each one is a place where polysilicon crosses active silicon.
54 contacts join metal to the polysilicon or active silicon under it.
63 vias join metal 2 to the metal under it.

Starting drawing for puzzle 98, Count to three and stop, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.