What is Programmable Logic Arrays ?
Combinational logic circuits are implemented using programmable logic devices such as programmable logic arrays (PLAs). A set of programmable AND gate planes, a set of programmable OR gate planes, and a set of programmable AND gate planes in the PLA can be conditionally complemented to produce an output. It should have M OR gates with programmable inputs from all of the AND gates for M PLA outputs, and it has 2N AND gates for N input variables. This pattern can be used to generate a wide variety of logic functions in the canonical forms of sum of products.
Programmable AND and OR gate planes are part of PLAs, as opposed to programmable array logic devices (PALs and GALs). The purpose of programmable logic arrays is to substitute a single chip with a limited number of NAND gates—roughly five to fifty—on a circuit board. In contrast, an FPGA board is built with enough gates to, say, implement a CPU. The PLA is a two-level AND and OR gate programmable logic device (PLD). PAL, on the other hand, only features a programmable AND gate and a fixed OR gate. PAL operates more quickly than PLA. Conversely, PLA functions more slowly than PAL.
What is Programmable Array Logic (PALs)?
Similar to a PLA, a Programmable Array Logic (PAL) is a PLD electronic device. PAL lacks programmable AND gates in favor of fixed OR gates, unlike PLA. It makes use of two straightforward functions, the number of linked AND gates to each OR gate determining the maximum number of product terms that can be formed in the SOP representation of the function. Despite the fact that the AND gates are always connected to the OR gates, the resulting product term is not shared with the output functions.
Design of Programmable Logic Array
A buffer, AND gate, and OR gate are utilized in PLA to build different combinational circuits. Only the necessary minterms are implemented in PLA; all other minterms are not realized. PLA offers greater flexibility because it features programmable AND and OR gate arrays, but its drawback is that it is difficult to operate. Three phases can be used to sum up how a PLA operates. First, the programming step Programming the input and output configurations into the PLA allows the user to define the logic function that the device will implement. The AND gate array receives the inputs and generates a set of product terms in the second stage, known as “product term generation.” Step three: Creating the sum term: The product terms are then used to create the output by applying them to the OR gate array.
Because PLAs are flexible and make it simple to implement complex functionalities, they are frequently employed in digital systems. As the arrays of AND and OR gates may be set up to handle a lot of inputs, they are very helpful for creating Boolean expressions with many of variables.
Design of Programmable Array Logic
The phrase “programmable array logic,” or “PAL,” refers to a particular kind of PLD known as a “programmable logic device circuit,” and it functions similarly to a PLA. Both programmable AND gates and fixed OR gates can be used in the design of the programmable array logic. This allows us to create two simple functions: the maximum number of product conditions that may be generated in the form of the sum of products (SOP) of an exact function is indicated by the associated AND gates with each OR gate.
The fact that logic gates such as AND are continuously coupled to OR gates suggests that the generated product term is not spread across the output functions. The main idea behind PLD development is to integrate complex Boolean logic onto a single chip by eliminating bad wiring, skipping the logic design, and using less power.
PLAs vs. PALs Features
- A PLA, or programmable logic device, is composed of an AND array and an OR array (PLD).
- Using the AND array, the desired logical function’s product terms are generated.
- The product terms are combined using the OR array to form the PLA’s output.
- Numerous logical operations can be implemented thanks to the programmable connections between the gates in the AND and OR arrays.
- PLAs are widely used in applications where flexibility is essential, including as computer CPUs and other digital logic circuits.
- PLAs are more flexible than PALs, but PALs are faster and less expensive.
- A PAL is a specific type of PLD that consists of an AND array and a fixed OR array.
- Unlike the OR array, the AND array is programmable.
- The AND array can be used to generate the product terms for the desired logical function.
- A fixed OR array is utilized to combine the product terms and produce the output for the PAL.
- PALs are commonly used in low-cost, small-scale applications such as embedded systems, when cost or speed are more important than flexibility.
- PALs are speedier and less expensive than PLAs, but they are less flexible.
PLAs vs. PALs Applications
- As a counter, PLAs are employed.
- PLAs are employed in decoding.
- The datapath is controlled by the use of PLAs.
- PLAs are used in input/output programming as a BUS interface.
- PLAs carry out the control logic of computer CPUs. Since the control logic is responsible for selecting the next instruction to be executed, it needs to be able to implement a broad variety of logical functions.
- PLAs are used to create a variety of digital logic circuits, such as multiplexers, registers, and decoders.
- Industry uses programmable logic controllers, or PLCs, to run machinery. PLAs are a great option for this application since they can carry out a variety of logical operations and are trustworthy and adaptive.
- PALs are quite safe.
- Designing PALs is incredibly flexible.
- PALs are quite effective.
- Compared to others, PALs are more dependable.
- PALs require less power to operate.
- It is less expensive to produce than PLA.
- Embedded systems are used in a wide range of products, such as toys, appliances, and cars. Because they must be inexpensive and both small and fast, PALs are a great choice for this application.
- Physical processes are monitored and controlled by the use of instruments. For this application, PALs are a great choice because they are easy to use, accurate, and dependable.
- Telecom networks have to manage a wide range of traffic. PALs are a great choice for this application due to their speed and scalability.
PLA vs. PAL
Conclusion of PLAs vs PALs
The OR gate array is the primary way that PALs and PLAs differ from each other. Whereas the OR gate array in PLAs is programmable, the OR gate array in PALs is fixed. PALs are easier to program than PLAs because of this distinction. Compared to PALs, PLAs can perform a greater range of logic operations.
Apart from the above mentioned matter, PLA and PAL are different in other aspects. Compared to PLA, PAL responds faster. On the other hand, PAL operates faster than PLA. Compared to PAL, PLA has more complexity. In contrast, PLA is more sophisticated than PAL. The PLA moves forward cautiously. In contrast, PAL moves swiftly. PAL is more expensive than PLA. Price-wise, PAL is less expensive than PLA. The PLA is more versatile than the PAL. In spite of this, PLA is more adaptable than PAL. More production and accessibility convenience is provided by the PAL. On the other hand, getting into the PLA is difficult. There aren’t many functions implemented in PLA. However, the great majority of PAL’s functions are currently functional.