Programmable Logic

PLDs contain programmable logic components called Logic Elements (LEs) and a hierarchy of reconfigurable interconnects that allow the LEs to be physically connected. You can configure LEs to perform complex combinational functions, or merely simple logic gates like AND and XOR. The logic blocks may also include memory elements, which may be simple flip-flops or more complete blocks of memory.

CPLDs are large-scale logic devices with up to thousands of programmable logic elements, non-volatile memory, and I/O block on one chip. Connections between the logic elements on these semiconductor chips are customized by the user with software tools. CPLD architecture has a predictable timing performance and speed, offers a range of logic capabilities, and is often employed in portable, battery-operated applications. FPGAs are denser and more complex than CPLDs and are used to implement larger or more complex designs.

A FPGA is not restricted to any predetermined hardware function. An FPGA allows you to program product features and functions, adapt to new standards, and reconfigure hardware for specific applications even after the product has been installed in the field—hence the name "field-programmable". Unlike previous generation FPGAs using Input and Output (I/O) with programmable logic and interconnects, today's FPGAs consist of various mixes of configurable embedded SRAM, high-speed transceivers, high-speed I/O, logic blocks, and routing.

PLDs have many design advantages, including rapid prototyping, shorter time to market, and the ability to re-program in the field. FPGAs have evolved from their primary use as a prototyping platform to wide use in mainstream volume production today.

FPGAs are advantageous for quickly bringing a complete hardware system up and operating because they are completely customizable and thus very flexible. Any number or type of peripherals can be programmed into the FPGA and the designer can create only what they need, versus buying an off-the-shelf processor with a unique blend of peripherals. Processors often include features that are not needed in a particular design, which can needlessly increase cost.

FPGAs usually come as a blank slate with a large library of building blocks that are implemented with accompanying engineering development tools and resources.

In an FPGA, a custom hardware system including peripherals must be designed, which is more complex a task than a ready-made processor or System-on-a-Chip (SoC). For FPGAs, the trade-off is design flexibility and speed-to-market, but they come with increased design complexity.

The lowest level of an FPGA is a Logic Element (LE). This building block has a lookup table and a small bit of storage. Along with these LEs, FPGAs contain clocks, Input and Output (I/O), memory and other more sophisticated blocks. Many FPGAs are integrated with a physical, embedded processor core, typically called a hard processor. A soft processor can be programmed using the FPGA’s logic, as well as memory, communication buses, peripherals, and various controllers. FPGAs are no longer just for prototyping. Both FPGAs and FPGA-based platforms are in wide use today and rival ASICs for selection in volume production.

Development tools can include hardware boards, schematics, cables, documentation, reference designs, example software code, an Integrated Development Environment (IDE, a kind of software platform/coding tool), Gerber files for printing the development board on additional PCBs later on, and hardware accessories, modules or daughter boards.

Development tools are also a critical sales tool. An excellent product will be set aside for another if development tools are insufficient or otherwise difficult to use. Manufacturers today often provide a website with a community forum so that people can locate documentation, share experiences, advice, tips, and get or give help.