Figure 4-80 is a combinational logic circuit that operates an alarm in a car whenever the driver and/or passenger seats are occupied and the seatbelts are not fastened when the car is started. The active-HIGH signals DRIV and PASS indicate the presence of the driver and passenger, respectively, and are taken from pressure-actuated switches in the seats. The signal IGN is active-HIGH when the ignition switch is on. The signal 

is active-LOW and indicates that the driver’s seatbelt is unfastened; 

is the corresponding signal for the passenger seatbelt. The alarm will be activated (LOW) whenever the car is started and either of the front seats is occupied and its seatbelt is not fastened.

(a) Verify that the circuit will function as described.

(b) Describe how this alarm system would operate if Z1-2 were internally shorted to ground.

(c) Describe how it would operate if there were an open connection from Z2-6 to Z2-10.

Figure 4-80

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