Puzzle 45 of 100

Letting go of a line

Goal

Make Y the inverse of A while E is high. While E is low, Y must keep its last level.

Die: 16 by 15 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: E, A
Output: Y
Supply: VDD
Ground: GND

New in this puzzle

An output that lets go

An inverter with one more switch in series in each half drives its output only while both switches are on. While they are off, neither rail reaches the output. Such an output is called tri-state.

Charge holds a level

A line that nothing drives keeps the charge on its capacitance, so it stays at its last level until something drives it again.

Hint

Build an inverter for A with one more transistor in each half. Put a P transistor between VDD and the inverter's P transistor with its gate on the inverse of E, and an N transistor between the inverter's N transistor and GND with its gate on E. The inverter for E is drawn.

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 45, Letting go of a line, 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 45, Letting go of a line, 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 45, Letting go of a line, 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

Metal67 squares
Polysilicon40 squares
Contact14 squares
N active10 squares
P active20 squares
N well64 squares
Input padE, A
Output padY
Supply padVDD
Ground padGND
Squares you draw, change, or erase56 squares

About the drawing

The drawing uses 145 of the die's 240 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 54 empty squares and change 2 drawn squares.
It forms 6 transistors: 3 N transistors and 3 P transistors. Each one is a place where polysilicon crosses active silicon.
14 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 45, Letting go of a line, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.