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

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

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

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

Decoder In general, there are n inputs and 2 n outputs We say the output line that detects the input pattern is asserted PatternLine Asserted

Decoder 2-bit decoder

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 2 n inputs for 2 n values, plus a set of n control lines as a binary bit pattern

Mux