Circuits: VLSI

Puzzle 92 of 100

One clock for both bits

Goal

Make Q1 and Q0 count 0, 1, 2, 3 and repeat, with both flip-flops on CLK. Q0 already toggles; give D1 the next value of Q1.

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

Next state logic

In a synchronous machine every flip-flop takes the same clock. Gates compute each flip-flop's next value from the present outputs, and all the bits change on the same edge.

Hint

Q1 changes only on the edges where Q0 is high, so the next Q1 is Q1 exclusive OR Q0. A pair of switches controlled by Q1 and QN1 can choose between Q0 and QN0.

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 92, One clock for both bits, 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 92, One clock for both bits, 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 92, One clock for both bits, 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

  • Metal320 squares
  • Polysilicon76 squares
  • Contact50 squares
  • N active27 squares
  • P active27 squares
  • N well111 squares
  • Metal 2436 squares
  • Via67 squares
  • Input padCLK, CLKN
  • Output padQ0, Q1
  • Supply padVDD, VDD
  • Ground padGND, GND
  • Squares you draw, change, or erase155 squares

About the drawing

  • The drawing uses 664 of the die's 1015 squares.
  • Part of the drawing is in place when the puzzle opens. To finish it, paint 126 empty squares and change 29 drawn squares.
  • It forms 20 transistors: 10 N transistors and 10 P transistors. Each one is a place where polysilicon crosses active silicon.
  • 50 contacts join metal to the polysilicon or active silicon under it.
  • 67 vias join metal 2 to the metal under it.
Starting drawing for puzzle 92, One clock for both bits, on a numbered grid.
The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.