CPLDs - Complex Programmable Logic Devices

 

CPLD stands for Complex Programmable Logic Device. As explained by the name, these are devices that have relatively higher complexity than the likes of PALs, but are less complex than FPGAs or Field Programmable Gate Arrays.

A CPLD is essentially made up of numerous macrocells, each of which consists of disjunctive normal form expressions as well as other logic operations for more specific applications for the purpose of logic implementation. Macrocells can be defined as the functional unit or building block of a Complex Programmable Logic Device which can perform combinational or sequential logic. They contain a combination of AND and OR gates arranged in an array which can be programmed to perform and execute a number of different logic functions.

CPLD Features

There are a number of features that CPLDs possess that makes them similar to other chips and devices in their category, but also sets them apart as a unique solution that is the optimum choice for certain scenarios and situations based on the requirements of the user. Here are some of the most important and defining features of CPLDs:

• CPLDs have a relatively large number of gates which make the implementation of more complex devices and programs possible. As compared to PALs which normally have gates ranging around a couple of hundred, CPLDs have thousands to over tens of thousands of gates.
• Special logic functions as well as complex interconnected feedback paths between the macro cells makes CPLD logic much more flexible and modifiable as compared to others.
• CPLD does not require an external configuration memory and therefore can start operating immediately after the system has been booted up. It is a type of non volatile configuration memory.
• They employ the use of Electrically Erasable Programmable Read Only Memory (EEPROM).
• Thanks to the non volatile and non ROM based configuration of the CPLDs, you do not have to worry about any unexpected delays or memory loss. The memory is retained in the circuit even when it has been powered down.
• CPLDs are also easy to reprogram at a very low cost, reducing your overall costs and expenditure while simultaneously improving the time to market of your products.
• The integrative and simplistic nature of CPLDs makes them a perfect fit in most kinds of design flows and architecture, posing very little trouble in terms of integration and design adjustments.
• They have low maintenance costs, proving to be a sound investment in the long run.
• The non volatile nature of CPLDs makes them a much more secure option as it is next to impossible to steal the stored design. The external memory of the FPGA devices have the potential to expose the IP, although the user can implement encryption techniques to combat this security threat.
• CPLDs are much better suited for deterministic timing analysis as opposed to FPGAs because of a lesser number of interconnects.