Puzzle 94 of 100

Load or hold

Goal

Make Q take the value of A on a rising edge of CLK while EN is high, and keep its value while EN is low.

Die: 30 by 29 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: CLK, CLKN, A, EN
Output: Q
Supply: VDD, VDD
Ground: GND, GND

New in this puzzle

Holding a value

A flip-flop takes D on every clock edge. Feeding its own Q back to D makes it keep its value, so a multiplexer in front of D chooses between keeping and loading.

Hint

Feed D from a pair of switches that pass A while EN is high and Q while EN is low. The switches need EN in both senses, so add an inverter for EN.

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 94, Load or hold, 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 94, Load or hold, 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 94, Load or hold, 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

Metal306 squares
Polysilicon53 squares
Contact35 squares
N active19 squares
P active19 squares
N well81 squares
Metal 2332 squares
Via49 squares
Input padCLK, CLKN, A, EN
Output padQ
Supply padVDD, VDD
Ground padGND, GND
Squares you draw, change, or erase320 squares

About the drawing

The drawing uses 547 of the die's 870 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 278 empty squares and change 42 drawn squares.
It forms 14 transistors: 7 N transistors and 7 P transistors. Each one is a place where polysilicon crosses active silicon.
35 contacts join metal to the polysilicon or active silicon under it.
49 vias join metal 2 to the metal under it.

Starting drawing for puzzle 94, Load or hold, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.