Puzzle 70 of 100

A latch from NAND gates

Goal

Make Q go high when SN is low and low when RN is low, and keep its level while SN and RN are both high.

Die: 20 by 12 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: SN, RN
Output: Q
Supply: VDD
Ground: GND

New in this puzzle

Inputs that act when low

A NAND gate's output is high whenever either input is low. In a NAND latch the inputs rest high and act when they go low, and their names end in N.

Hint

Draw a second NAND gate to the right of the first. Join Q to one of its inputs and bring RN to the other, then join its output back to the free input of the first gate.

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 70, A latch from NAND gates, 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 70, A latch from NAND gates, 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 70, A latch from NAND gates, 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

Metal93 squares
Polysilicon42 squares
Contact20 squares
N active16 squares
P active32 squares
N well80 squares
Metal 219 squares
Via4 squares
Input padSN, RN
Output padQ
Supply padVDD
Ground padGND
Squares you draw, change, or erase82 squares

About the drawing

The drawing uses 191 of the die's 240 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 75 empty squares and change 7 drawn squares.
It forms 8 transistors: 4 N transistors and 4 P transistors. Each one is a place where polysilicon crosses active silicon.
20 contacts join metal to the polysilicon or active silicon under it.
4 vias join metal 2 to the metal under it.

Starting drawing for puzzle 70, A latch from NAND gates, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.