Puzzle 95 of 100

Divide by three

Goal

Make Q0 high for one clock period in every three, and Q1 follow Q0 one clock period later.

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

New in this puzzle

A shorter cycle

Two flip-flops have four states. Next state logic can leave one of them out, so the machine repeats every three clocks, and from the unused state it falls back into the cycle.

Hint

Join Q0 to D1. Feed D0 from a NOR gate of Q0 and Q1, so that Q0 goes high only after both bits were low.

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 95, Divide by three, 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 95, Divide by three, 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 95, Divide by three, 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

Metal285 squares
Polysilicon74 squares
Contact47 squares
N active27 squares
P active27 squares
N well111 squares
Metal 2330 squares
Via58 squares
Input padCLK, CLKN
Output padQ0, Q1
Supply padVDD, VDD
Ground padGND, GND
Squares you draw, change, or erase101 squares

About the drawing

The drawing uses 587 of the die's 1015 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 92 empty squares and change 9 drawn squares.
It forms 20 transistors: 10 N transistors and 10 P transistors. Each one is a place where polysilicon crosses active silicon.
47 contacts join metal to the polysilicon or active silicon under it.
58 vias join metal 2 to the metal under it.

Starting drawing for puzzle 95, Divide by three, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.