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NOR gate

Digital logic · Beginner · about 10 minutes · part of Zen’s Electronics Design Mastery

OR followed by NOT: the output is 1 only when both inputs are 0. NOR is also universal; the Apollo guidance computer was built entirely from NOR gates.

NOR gate: the circuit on the simulator's bench

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How it works

Y = (A + B)̅

ABYbench
001—
010—
100—
110—

Flip the switches to try every row. “bench” fills in with what the chip actually did.

74HC02: quad 2-input nor in one 14-pin chip. Pin 14 is +5 V, pin 7 is ground. Every unused input should be tied to VCC or GND in a real build.

Try it on the bench

  1. Click switches 1 and 2 to step through 00, 01, 10 and 11. Each combination fills a row of the table.
  2. Select U1 and change its family to 74LS: the high output drops to about 3.5 V, because TTL outputs cannot pull all the way to VCC.
  3. Delete the wire to input B. A floating CMOS input is undefined: the output flickers. Switch the chip to 74LS and the floating input reads as 1.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Digital Electronics”.

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