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These are the Lecture Notes of Digital Circuits and Systems which includes Present State, Principle, Memory Elements, Elementscombinational Logic, Description, Circuit and Create, Number of States, Binary Codes, Letter Symbol etc. Key important points are: Digital Circuitry, Programmable Logic Devices, Implement, Discrete Gates, Logic Functions, Difficult to Minimise, Single Device, Expensive, Performance, Custom Logic
Typology: Study notes
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Fixed
AND
array
Blow fuses on all non required connections
PLA – Programmable AND and OR arrays
PLA Eg
Unwanted connections are "blown"
Equations
Programming
1 = asserted in term
0 = negated in term
- = does not participate
1 = term connected to output
0 = no connection to output
Input Side:
Output Side:
F0 = A + B' C'
F1 = A C' + A B
F2 = B' C' + A B
F3 = B' C + A
A given column of the OR array has access to only a subset of the possible product terms
PROM
Not unlike a PLA
structure with a
fully decoded
AND array!
ROM vs. PLA:
ROM approach advantageous when
(1) design time is short (no need to minimize output functions)
(2) most input combinations are needed (e.g., code converters)
(3) little sharing of product terms among output functions
ROM problem: size doubles for each additional input, can't use don't cares
PLA approach advantangeous when
(1) design tool like espresso is available
(2) there are relatively few unique minterm combinations
(3) many minterms are shared among the output functions
PAL problem: constrained fan-ins on OR planes
Complex PLD
X3000 series Configurable Logic Block
FPGA Design: