Digital Logic Structures: Chapter 3

1. 1 Digital Logic Structures: Chapter 3 COMP 2610 Dr. James Money COMP 2610

2. Combinational Logic Circuits • From these basic logic gates, we can now build more advanced logic circuits • We will only use the AND, OR, and NOT gates for now

3. Combinational Logic Circuits • There are two types of logic structures: • Ones that store information – such as a bit of memory • Ones that do not – these are usually called decision elements or combinational logic circuits • We consider the combination logic circuits of a decoder, mux, and a full adder

4. Decoder • A decoder is a circuit whose property is that one of it’s outputs is 1 and the rest are 0 • The input values are consider as a bit pattern • For 2 bits, there are 4 possible values • The output is the correctly selected value

5. Decoder • In general, there are n inputs and 2noutputs • We say the output line that detects the input pattern is asserted

6. Decoder 2-bit decoder

7. Mux • The next logic structure we consider is called a multiplexer, or more commonly a mux • The function of a mux is to select one of the inputs and connect it to the output line • There are 2n inputs for 2n values, plus a set of n control lines as a binary bit pattern

8. Mux

9. Mux