Experiment 7 ELEE 2130
Objective
To investigate the operation of the NOR and NAND gate latches.
Reference
Chapter 7.
Parts Needed
7400(2). 7402(2), 7474, and 7476 ICs.
Prelab
Fill out all questions/blank spaces /tables on this handout before coming to the lab. Use your
lab notebook.
Procedure
1. NOR gate Set-Reset latch
(a) Wire the NOR gate latch as shown in Figure. Connect the normally-Low pushbutton
switches to the Set and Reset inputs to the circuit. You will monitor circuits Q and P
(=Q’) with LED monitors.
(b) Turn the power supply ON, and note the states of both LEDs: Q = ____; Q’ = ____.
Predicting the states of a sequential device when power is first applied is impossible,
so the value thus recorded are random. CLEAR (reset) Q by momentarily pulsing the
RESET input HIGH. If Q is already LOW, pulsing the RESET input will have no
effect on this circuit.
(c) Pulse the SET input HIGH, and observe the effect on the circuit outputs: Q = ______;
Q’ = ______. Note that releasing the pushbutton does not cause Q to change from its
new state. Why? ______________________________________________________.
Now pulse the SET input HIGH again. What effect does it have on the circuit
outputs: ____________________________________________________________.
(d) Pulse the RESET input HIGH, and observe that Q changes back to LOW and stays
LOW even after the pushbutton is released.
(e) Alternately, pulse the SET and RESET inputs HIGH several times. Note that the
outputs are always at opposite states.
(f) Press and hold the SET and RESET inputs HIGH at the same time. Record the
outputs: Q = ____; Q’ = ______. Are they opposite of each other? __________.
Release the pushbuttons, and note the states of the outputs: Q = ______; Q’ = ______
Are they opposite or equal? __________.
