Chapter 4: Combination Logic

Chapter 4: Combination Logic

1. Definition

   • No feedback loops, no clock, output appears shortly after changed input.

2. Analysis procedure

3. Design procedure

   • Determine number of required inputs and outputs
   • Derive truth table
   • Obtain simplified boolean functions
   • Draw logic diagram and verify

4. * Adders, subtractors, comparators

   • Review lab

5. MUX

6. Decoder

   • Sometimes called a minterm generator
     • From a sum of minterm equation for a function -- we can use a decoder to implement that function
   • Active high
     • Implemented with AND gates
     • Only one output is 1, the rest are 0
     • EN has to be 1 for it to produce outputs
   • Active low
     • Implemented with NAND gates
     • Only one output is 0, the rest are 1
     • EN has to be 0 for it to produce outputs

7. Encoder

   • Takes 2^n lines outputs n, opposite of decoder
   • Priority decoder
     • Gets over the problem of undefined output when more than one input is on by...
       • Treating the input with highest number as highest priority
       • A v output for when any of the inputs is 1