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DLD UNIT-6
-Ramaiah Thalluri-PACE Institute of Technology & Sciences, Ongole
-Andhra Pradesh, INDIA
PLD’s (Programmable Logic Devices)
An IC that contains large numbers of gates, flip-flops, etc. that can be configured by the user to perform different functions is called a Programmable Logic Device (PLD).
PLD’S ...
PLDs are typically built with an array of AND gates (AND-array) and an array of OR gates (OR-array).
PLD – General Structure :
Types of standard PLDs:
PROMPALPLA
IC’s (Integrated Circuits) A large number of components
fabricated on a single chip is called an IC.
Types of IC’s SSI - Small Scale Integration MSI – Medium Scale Integration LSI - Large Scale Integration VLSI – Very Large Scale Integration ULSI – Ultra Large Scale Integration
ROM (Read Only Memory) ROM is a memory device in which
permanent binary information is stored.
Types of ROM’s MROM – Mask Programmable ROM PROM – Programmable ROM EPROM – Erasable PROM EEPROM – Electrically Erasable PROM
Conventional & Array logic symbol
Buffer/Inverter
Programming by blowing fuses.
OR - PLD Notation
AND - PLD Notation
Three Fundamental Types of PLDs:
The ROM (Read Only Memory) or PROM (Programmable Read Only Memory):
The input lines to the AND array are hard-wired and the output lines to the OR array are programmable.
Each AND gate generates one of the possible AND products (i.e., minterms).
ROM block diagram:
PLA... The AND and OR gates inside the
PLA are initially fabricated with the links (fuses) among them.
Block diagram of the PLA
Block diagram of the PLA ... The product terms constitute a group
of k AND gates each of 2n inputs. Links are inserted between all n
inputs and their complement values to each of the AND gates.
Links are also provided between the outputs of the AND gates and the inputs of the OR gates.
Another type-Block diagram of the PLA
PLA . . .
In every PLA, we have to design the Personality matrix or Programming table of given example.
Example is shown below.
Consider an example & the outputs are shown below.
PLA - Before Programming
PLA - After Programming
PLA - Alternate representation
PLA as ROM :
Programmable Logic Gate Arrays