Unit 5 Programmable Logic Devices.pdf
- 1. Unit 5 Digital Electronics (Programmable Logic Devices)
- 2. Introduction • Programmable Logic Devices PLDsPLDs are the integrated circuits. They contain an array of AND gates & another array of OR gates. • There are three kinds of PLDs based on the type of arrayss, which has programmable feature. – Programmable Read Only Memory – Programmable Array Logic – Programmable Logic Array • The process of entering the information into these devices is known as programming. • Basically, users can program these devices or ICs electrically in order to implement the Boolean functions based on the requirement. • Here, the term programming refers to hardware programming but not software programming.
- 3. Programmable Read Only Memory • Read Only Memory ROMROM is a memory device, which stores the binary information permanently. That means, we can’t change that stored information by any means later. • If the ROM has programmable feature, then it is called as Programmable ROM PROM. • The user has the flexibility to program the binary information electrically once by using PROM programmer. • Read Only Memory ROMROM is a memory device, which stores the binary information permanently. • That means, we can’t change that stored information by any means later. If the ROM has programmable feature, then it is called as Programmable ROM PROM. • The user has the flexibility to program the binary information electrically once by using PROM programmer.
- 4. Block Diagram Of PROM
- 5. Example Of PROM Let us implement the following Boolean functions using PROM. A(X,Y,Z)=∑m(5,6,7)A(X,Y,Z)=∑m(5,6,7) B(X,Y,Z)=∑m(3,5,6,7)B(X,Y,Z)=∑m(3,5,6,7)
- 6. Detailed Circuit Diagram Of PROM
- 7. • PAL is a programmable logic device that has Programmable AND array & fixed OR array. • The advantage of PAL is that we can generate only the required product terms of Boolean function instead of generating all the min terms by using programmable AND gates. • Here, the inputs of AND gates are programmable. That means each AND gate has both normal and complemented inputs of variables. • So, based on the requirement, we can program any of those inputs. • So, we can generate only the required product terms by using these AND gates. • Here, the inputs of OR gates are not of programmable type. • So, the number of inputs to each OR gate will be of fixed type. • Hence, apply those required product terms to each OR gate as inputs. Therefore, the outputs of PAL will be in the form of sum of products form. Programmable Array Logic PAL
- 8. Block Diagram Of PAL
- 9. Example of PAL Let us implement the following Boolean functions using PAL. A=XY+XZ′ A=XY′+YZ′
- 10. Programmable Logic Array • PLA is a programmable logic device that has both Programmable AND array & Programmable OR array. Hence, it is the most flexible PLD. • Here, the inputs of AND gates are programmable. That means each AND gate has both normal and complemented inputs of variables. • So, based on the requirement, we can program any of those inputs. • So, we can generate only the required product terms by using these AND gates. • Here, the inputs of OR gates are also programmable. • So, we can program any number of required product terms, since all the outputs of AND gates are applied as inputs to each OR gate. • Therefore, the outputs of PAL will be in the form of sum of products form.
- 11. Block Diagram Of PLA
- 12. Example Of PLA Let us implement the following Boolean functions using PLA. A=XY+XZ′ B=XY′+YZ+XZ′