Programmable logic array (pla)

Worth seeing slides on PLA.

1. Programmable Logic Array (PLA) Digital Logic and Design BSCS 2 nd (MA) Group 2

2. Programmable logic devices (pld’ s ) Special type of IC Contains array of AND gates and OR gates Programmable

3. C ombinational pld’ s A combinational PLD is an IC that provide an AND-OR sum of product implementation. It has three types: PROM (Programmable Read Only Memory) PAL (Programmable Array Logic) PLA (Programmable Logic Array)

4. Comparison of PAL, P rom and pla PAL: Programmable AND array and fixed OR array. PROM: Fixed And array which is construction as a decoder and programmable OR array. PLA: Both the AND array and OR array can be programmed.

5. What is pla? It has both the AND arrays and OR arrays that can be programmed. Block diagram of PLA:

6. Operators of PLA Buffer: A buffer has only a single input and a single output with behavior that is the opposite of an  NOT gate. It simply passes its input, unchanged, to its output.

7. Continued… AND gate: A HIGH output (1) results only if all the input to the AND gate are HIGH (1). OR gate: A HIGH output (1) results if one or both the inputs to the gate are HIGH (1).  XOR gate: A HIGH output (1) results if (1) occurs only one time.

8. Implementation of PLA Question: F1(A, B, C)=∑ ( 2,4,5,7) F2(A, B, C)= ∑(0,1,2,4,6)

9. Simplify using K-MAp F1=A’BC’+AC+AB’ F2=A’B’+C F1’=(ABC’+A’B’+AC’) F2’=(AC+BC)’

10. PLA Programmable Table

11. Circuit Diagram

12. Advantages of pla Less time consuming Easy to check and change Adaptive to new technology Connection mask

13. Disadvantages of pla Less speed Larger chip area Expensive

14. Applications of pla Micro-processor chip Control logic Code conversions Micro-programmable code conversions Decision tables Bus priority resolvers Memory overlay

15. Questions