Circuits: VLSI

Puzzle 79 of 100

A reset on the clock

Goal

Make Q change level at every rising edge of CLK, except that a rising edge while R is high makes Q low.

Die
40 by 14 squares
Layers
Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs
CLK, R
Output
Q
Supply
VDD
Ground
GND

Go to the solution

New in this puzzle

A synchronous reset

A reset that acts through D takes effect at the next rising edge of the clock. It gives the flip-flop a known level, so Q can be judged against a target from the first edge.

Hint

Replace the inverter that feeds D with a NOR gate of Q and R. While R is high the NOR gate holds D low, so the next rising edge stores a 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 79, A reset on the clock, 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 79, A reset on the clock, 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 79, A reset on the clock, 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

  • Metal206 squares
  • Polysilicon142 squares
  • Contact45 squares
  • N active35 squares
  • P active70 squares
  • N well160 squares
  • Metal 277 squares
  • Via11 squares
  • Input padCLK, R
  • Output padQ
  • Supply padVDD
  • Ground padGND
  • Squares you draw, change, or erase47 squares

About the drawing

  • The drawing uses 457 of the die's 560 squares.
  • Part of the drawing is in place when the puzzle opens. To finish it, paint 14 empty squares, change 29 drawn squares, and erase 4 squares.
  • It forms 18 transistors: 9 N transistors and 9 P transistors. Each one is a place where polysilicon crosses active silicon.
  • 45 contacts join metal to the polysilicon or active silicon under it.
  • 11 vias join metal 2 to the metal under it.
Starting drawing for puzzle 79, A reset on the clock, on a numbered grid.
The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.