Puzzle 80 of 100

A shift register

Goal

Make Q1 take the level of D at each rising edge of CLK, and Q2 take the level Q1 had just before the same edge.

Die: 58 by 14 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: CLK, D
Outputs: Q1, Q2
Supply: VDD
Ground: GND

New in this puzzle

Flip-flops in a chain

Flip-flops on one clock pass a level one place along at each rising edge. Each takes the level its neighbor had just before the edge, so a level moves one stage per clock period.

Hint

Draw the switch of the second flip-flop's first latch, from the contacts of Q1 to the latch beside them. It must be open while CLK is low, like the first switch of the first flip-flop.

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 80, A shift register, 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 80, A shift register, 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 80, A shift register, 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
Polysilicon220 squares
Contact62 squares
N active54 squares
P active108 squares
N well232 squares
Metal 2122 squares
Via15 squares
Input padCLK, D
Output padQ1, Q2
Supply padVDD
Ground padGND
Squares you draw, change, or erase15 squares

About the drawing

The drawing uses 676 of the die's 812 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 5 empty squares and change 10 drawn squares.
It forms 26 transistors: 13 N transistors and 13 P transistors. Each one is a place where polysilicon crosses active silicon.
62 contacts join metal to the polysilicon or active silicon under it.
15 vias join metal 2 to the metal under it.

Starting drawing for puzzle 80, A shift register, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.