Programmable Logic Array(PLA) & Programmable Array Logic(PAL)

General architecture and problems on Programmable Logic Array(PLA) & Programmable Array Logic(PAL)

1. Review:
General Structure
Problems based on PLA & PAL
Kongunadu College of Engineering & Technology PLA & PAL 1

2. PLA(Programmable Logic Array)
PLA is similar to PROM but it does not provide full decoding
of the variables and does not generates all the minterms.
The PLA replaces decoder by a group of AND gates, each of
which can be programmed to generate a product term of the
input variables.
There are three set of fuses present:
 between n-inputs & their complement values
 between the output of the AND gates and input of the OR gates.
 third set allows the output function to be generated either in AND-
OR-INVERT form or in the AND-OR form.

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3. Block Diagram
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4. PAL(Programmable Array Logic)
It is a programmable logic device with a fixed OR
array and a programmable AND array.
Since only AND gates are programmable, the PAL is
easier to program but it is not flexible as PLA.

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5. 5 Kongunadu College of Engineering & Technology PLA & PAL

6. Difference between PAL & PLA
PAL PLA
Both AND and OR arrays are
programmable.
OR array is fixed and AND array is
programmable.
Only desired minterms are
programmed using AND array.
Only desired minterms are
programmed using AND array.
Cheaper and Simpler Costliest and complex than PAL and
PROMs
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7. Example

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9. 9 Kongunadu College of Engineering & Technology PLA & PAL

10. Implementation
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11. References:
Mandal, “Digital Electronics Principles & Application,
McGraw Hill Edu, 2013.
William Keitz, Digital Electronics-A Practical Approach with
VHDL, Pearson, 2013.
Thomas L.Floyd, ‘Digital Fundamentals’, 11th edition, Pearson
Education, 2015.
Charles H.Roth, Jr, Lizy Lizy Kurian John, ‘Digital System
Design using VHDL, Cengage,2013.
D.P.Kothari,J.S.Dhillon, ‘Digital circuits and Design’,Pearson
Education, 2016.
A.P.Godse., Dr.D.A.Godse, ‘Digital Logic Circuits’ , Technical
Publications Third Edition 2016
Other Web Sources

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