Multiplexers,
Demultiplexers ( Decoders),
and Encoders
Some of the coolest circuit names in all of EE

EE481 Logical Design Lab
Fall 2003, Lab #2

Prelab Questions

1. Design a 3-select line multiplexer from 2-select line multiplexers.
2. Show a 3-select line multiplexer implementing:

   

3. Show a 2-select line multiplexer implementing the above expression
4. Show the use of a 74148 as an interface for a computer connected to 5 devices. The circuit should operate as follows:
   • Each device will assert a ``request for service'' line when they require service (e.g., a keyboard with a key press).
   • The computer requires a single request for service line and a 3-bit code specifying the device that requires service.
   • Thus, the circuit has 5 inputs and 4 outputs.
   For this circuit where would you connect a high-priority device like a modem compared to a low-priority device like a CRT (name a pin on the 74148 for each)?

Experiments

1. Implement a circuit for the following 3 functions using only a 74138 and NAND gates:

   

   

   

2. Implement the same circuit with two levels of logic (the normal SOP way). Compare the number of wires required for each implementation.