Puzzle 56 of 100

An even ring

Goal

The ring of four stages does not repeat. Make Y repeat with a period between 10 and 22 ns once EN is high.

Die: 28 by 15 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Input: EN
Output: Y
Supply: VDD
Ground: GND

New in this puzzle

An even ring holds

In a ring of an even number of inverting stages, each stage agrees with the stage after it, so the ring settles in one of two states and stays there. Such a ring stores a level instead of repeating it.

Hint

A ring of four inverting stages settles with each stage holding the one after it. Close the ring from the output of another stage instead, so that it passes through an odd number of inverting stages.

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 56, An even ring, 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 56, An even ring, 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 56, An even ring, 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

Metal156 squares
Polysilicon77 squares
Contact40 squares
N active17 squares
P active34 squares
N well104 squares
Input padEN
Output padY
Supply padVDD
Ground padGND
Squares you draw, change, or erase19 squares

About the drawing

The drawing uses 270 of the die's 420 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 5 empty squares, change 5 drawn squares, and erase 9 squares.
It forms 12 transistors: 6 N transistors and 6 P transistors. Each one is a place where polysilicon crosses active silicon.
40 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 56, An even ring, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.