Programmable Logic Devices(PLDs) Basics: Types, Applications and Examples

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What are PLDs?

The term "programmable logic device" refers to an integrated circuit that has a variety of logic components and connections that may be programmed by the user to perform certain logic functions. Simple combinational or sequential circuits, like AND, OR, NOT, and XOR gates, or registers are frequently used as the logic components. The connections are frequently made using programmable switches or multiplexers, which can connect the inputs and outputs of the logic units in various ways. A hardware description language (HDL), such as Verilog or VHDL, or a graphical user interface (GUI) software tool can be used to program a PLD. Then, the PLD is updated with the programming code or file using a specialized device programmer or a common interface like JTAG or USB. The configuration of the logic components and their connections to carry out the desired logic function is dictated by the programming code or file.

What are PLDs?

History of PLDs

In the late 1960s and early 1970s, the first programmable logic devices (PLDs) were introduced. These devices were built using a variety of methods, such as floating-gate UV erasable PROMs (EPROMs), programmable read-only memories (PROMs), and mask-programmable gate arrays (MPGAs). Motorola unveiled the XC157, an MPGA having 30 uncommitted input/output pins and 12 gates, in 1969. In order to program the XC157, changes were made to the metal layer as the IC was being made. Texas Instruments created the IBM read-only associative memory, or ROAM, based MPGA called the TMS2000 in 1970. The TMS2000 contained 8 JK flip flops for memory and up to 17 inputs and 18 outputs. For this device, TI created the term Programmable Logic Array (PLA). A PLD based on the cutting-edge PROM technology was being developed by General Electric Company (GE) in 1971. By allowing multilevel logic, this experimental gadget outperformed IBM's ROAM. The first erasable PLD ever created was the GE gadget. The DM7575, a mask-programmable PLA device with 14 inputs and 8 outputs but no memory registers, was released by National Semiconductor in 1973. Although this device was more widely used than the TI component, its use was constrained by the high cost of the metal mask. The 82S100 field programmable logic array (FPGA), created by Signetics in 1975, was based on the DM7575. In order to create a mask-programmable logic device incorporating the GE advances, GE and Monolithic Memories (MMI) entered into a contract in 1974. The PALA, or "Programmable Associative Logic Array," was the name of the gadget. The MMI 5760, which was finished in 1976, could build multilevel or sequential circuits with more than 100 gates. The device was supported by a GE design environment where Boolean equations would be transformed into mask patterns for customizing the device. The MMI 5760 was never commercially available though.

Types of PLDs

Programmable logic arrays (PLAs): The most straightforward kind of PLDs are programmable logic arrays (PLAs). They are made up of a series of AND gates followed by OR gates. The product phrases are created using AND gates, and they are added together using OR gates.

Programmable logic arrays (PLAs)

Programmable array logic (PALs): PLAs are comparable to programmable array logic (PALs), except PALs have a fixed OR gate array. Due to this, they are simpler to program than PLAs. The OR gates are fixed, but the AND gates are programmable.

Programmable array logic (PALs)

Generic array logic (GALs): In contrast to PALs, generic array logic (GALs) has a programmable OR gate array. They have more flexibility as a result than PALs. Programmability is available for both the AND and OR gates.

Generic array logic (GALs)

Complex programmable logic devices (CPLDs): CPLDs, or complex programmable logic devices, are more complex than PLDs. They might have a few hundred or perhaps a few thousand gates. A programmable AND gate array and a programmable OR gate array are frequently found in CPLDs.

Complex programmable logic devices (CPLDs)

Field-programmable gate arrays (FPGAs): The most intricate PLD design. They can be configured to implement a huge range of logic functions and have millions of gates. FPGAs are frequently utilized for demanding and intricate applications.

Field-programmable gate arrays (FPGAs)

Video related to PLDs

How PLDs Work?

Flip flops, AND gates, and OR gates are just a few of the logic components included in programmable logic devices that may be customized by the user. When programming is being done with a specialized software program, the user may alter the internal connections and logic. Occasionally, programmable logic devices include a number of fuses that were present in the original, unprogrammed PLD. To make the connections permanent in a certain configuration as per your design, you effectively blow out the fuses when programming the logic device and verifying the linkages. You must use the appropriate software and language to interface with the technology in order to program a programmable logic device. Most likely, a hardware description language, or HDL, will be used by you. Verilog or VHDL are two examples of higher level languages that can be used for sophisticated devices. In order to transfer the logic pattern you have created in the provided hardware language onto the Programmable logic device, you would also need a device programmer.

Advantages of PLDs

Digital Systems Design: Designing digital systems, including microprocessors, microcontrollers, digital signal processors, embedded systems, computer peripherals, communication devices, etc., involves the use of PLDs. PLDs provide more design flexibility than discrete logic devices when it comes to creating sophisticated logic functions with less hardware and wire.
Rapid prototyping: PLDs are used to quickly and easily prototype digital systems without the need for costly fabrication processes or protracted development cycles. PLDs enable instantaneous testing and debugging of digital systems by altering their programming without changing their physical makeup.
Reconfigurability: PLDs are used to dynamically reconfigure digital systems in response to shifting requirements or environmental conditions without the need to replace or modify hardware. By permitting switching between several modes or functionalities based on the input data or external signals, PLDs provide adaptive computing.
Performance: PLDs outperform fixed logic devices in terms of speed, power consumption, reliability, and scalability. PLDs make it possible to accomplish several tasks at once while utilizing various components of the device.
Cost-effectiveness: PLDs are more economical than fixed logic devices in terms of design time, development costs, maintenance costs, and product life cycles. By enabling the reuse of pre-existing code modules and libraries for various applications, PLDs decrease design time. PLDs lower development costs by enabling simple customization and error repair without the need for hardware upgrades. By enabling simple upgradeability and compatibility with new technologies without requiring hardware changes, PLDs lower maintenance expenses. PLDs provide functionality and feature addition without requiring hardware changes, extending the product life cycle.

Applications of PLDs

Digital signal processing: Filters, modulators, and demodulators are just a few of the algorithms that are implemented using PLDs in digital signal processing.
Communication: Systems for communication, including modems, routers, and switches, use PLDs.
Control systems: PLDs are used to create control systems, such as those used in industrial automation and robotics.
Data gathering: PLDs are used to gather information from sensors and other gadgets.
Equipment for testing and measuring, including oscilloscopes and logic analyzers, uses PLDs.
Medical devices: PLDs are a component of medical equipment including pacemakers and defibrillators.
Aerospace and defense: PLDs are utilized in avionics and radar systems, among other aerospace and defense applications.
Consumer electronics: PLDs are a component of consumer electronics like TVs, DVD players, and digital cameras.

Examples of PLDs

XC9500 series: Xilinx's XC9500 series is a family of CPLDs. Up to 5120 gates of the XC9500 series can be programmed in-system.

XC9500 series

Altera MAX 7000 series: The MAX 7000 series from Altera is a group of CPLDs. Up to 28,000 gates in the MAX 7000 series can be programmed in-system.

Altera MAX 7000 series

Lattice ECP5: Lattice Semiconductor makes the Lattice ECP5 line of FPGAs. The ECP5 can be programmed in-system and has up to 2 million gates.

Lattice ECP5

Intel Stratix 10: This is a class of FPGAs from Intel called Stratix 10. The Stratix 10 may be programmed in-system and has up to 18 million gates.

Intel Stratix 10

Xilinx Virtex UltraScale+: The Xilinx Virtex UltraScale+ family of FPGAs is one example. Up to 180 million gates on the Virtex UltraScale+ can be programmed in-system.

Xilinx Virtex UltraScale+

Conclusion

PLDs, which are adaptable electronic parts, can be used to implement a huge range of different digital logic functions. Compared to custom-designed ICs, they are simpler to design, less expensive, and smaller. PLDs are employed in many different fields, such as consumer electronics, telecommunications, industrial control systems, and computers.