What is CPLD?
Complex Programmable Logic Devices (CPLDs) are integrated circuits (ICs) that can be used in place of circuits constructed from multiple logic ICs. The logic in a CPLD can be altered repeatedly without requiring a PCB modification, unlike discrete logic IC circuits.
The fundamental component of a CPLD (Complex Programmable Logic Device) is a
programmable interconnect matrix cell surrounded by programmable logic macrocells (MC).
The MC structure stands out among them as being the most complicated and having a complex I/O cell interconnection structure that may be constructed by the user based on the requirements of a particular circuit structure to carry out certain duties. The developed logic circuits are time-predictable because the CPLD uses fixed-length metal wires for the internal connections of each logic block, avoiding the drawback that the timing of the segmented interconnection structure is not entirely predictable.
Development History of CPLD
The PLD, the first programmable logic device, was created in the 1970s. PLDs are integrated
circuits (ICs) with a large number of flip-flops and logic gates that may be programmed to carry out a variety of tasks. The simplest Programmable Logic Device consists of an array of AND and OR gates, and both the logic of the array and the connections between the gates may be programmed. PLDs can be broadly categorized into three groups. Field programmable gate arrays (FPGA), Simple Programmable Logic Devices (SPLD), and Complex Programmable Logic Devices (CPLD).
The design of its hardware structure was far more flexible than that of pure hardware digital circuits since it could be accomplished by software. However, due to their too-simplistic construction, they could only implement small-scale circuits. PLDs can only construct small-scale circuits, thus complex programmable logic devices, or CPLDs, were first introduced in the middle of the 1980s to address this limitation.
CPLD Features
Flexible programming, high integration, a quick design and development cycle, broad
applicability and improved development tools are all characteristics of CPLD.
Additionally, CPLD provides advantages like minimal design and production costs, low
hardware experience requirements for designers, no testing necessary for standard goods, great confidentiality, and a widely accepted price, among others.
CPLD is frequently used in product prototyping and product manufacturing (typically below
10,000 pieces) because it can realize bigger-scale circuit design.
A CPLD’s internal structure comprises of macrocells and a programmable AND/OR array.
Non-volatile memory: If the CPLD’s power is turned off, the logic design that has been
loaded into it will not be lost. When the CPLD’s power is turned on, the logic circuit will be
ready.
Physically (number of pins/IC package size) and logically (number of gates and macrocells),
CPLDs come in a variety of sizes.
PLD vs CPLD
They could only be used to implement small-scale circuits because of their overly simple architecture. Complex programmable logic devices, or CPLDs, were first introduced in the middle of the 1980s to overcome the constraint that PLDs can only build small-scale circuits. Because of its changeable hardware, PLDs deliver higher performance and versatility. One of the three main categories of PLDs, along with SPLDs and FPGAs, is CPLDs. The performance and complexity of CPLDs fall between that of SPLDs and FPGAs.
CPLD vs. FPGA
CPLD is better suited for small- to medium-sized applications than FPGA is for sophisticated ones. Furthermore, CPLDs are more adept at predicting delays than FPGAs. The nonvolatile internal memory of the CPLD makes it more secure than the FPGA. CPLD is an integrated circuit that supports the implementation of digital systems, as opposed to FPGA, which is an integrated circuit meant to be modified by a customer or a designer after production.
The logic resource is an additional major differentiator between CPLD and FPGA. While CPLD offers the barest minimum in logic resources, FPGA provides an enormous quantity of logic resources and storage components to develop complex systems. CPLD and FPGA use varying amounts of electricity; CPLD uses less power than FPGA, which uses more. The FPGA is more expensive than CPLDs, but CPLDs are more cost-effective.
When to use CPLD?
When a design necessitates the use of multiple 7400 series logic ICs, think about employing a
CPLD. For simpler PCBs, a CPLD will be more affordable, quicker, and programmable with the ideal pin-out arrangement. When creating complex designs that may take numerous iterations, use CPLDs. Designing, etching, and stuffing a new circuit board is more difficult than simply designing a new circuit in software and uploading it to the CPLD.
If you want maximum speed and quick response, choose a CPLD. Amazingly, CPLDs start at 100MHz whereas microcontrollers only respond to interrupts at a few MHz. CPLD designs produce circuits that react almost immediately to external stimuli. When a microcontroller runs code to react to events, even interrupt procedures have a noticeable lag.
How to use CPLD?
Computers are used for the majority of the CPLD’s work. Draw a schematic diagram, write hardware description language (VHDL, Verilog), compile, give the input excitation signal of the logic circuit, simulate, and confirm that the logic output result is correct. 64 of the 7128 input and output pins can be configured for carry-out pin input and output locking. Generate code. Transfer and store the code in the CPLD chip using the download cable. Pins for 7128 chips have been added. The wire connects the digital tube, quiz switch, indicator, and buzzer to the chipboard.
The CPLD chip system interface circuit is then powered on for testing. The matching bit’s indicator light should be lit when the quiz switch is depressed. The referee will add points once the response is accurate before determining if the digital display is accurate at this stage. In order to fix any issues, you can edit the hardware description language or schematic diagram once again.
After the design is complete, you can immediately clone additional CPLD chips for mass production; that is, the code can be written. If you wish to create additional designs for the chip, such as traffic light designs, you must redo the work described above and sketch the schematic diagram or write the hardware description language once more. This design change is comparable to redecorating a home, and CPLDs allow for tens of thousands of iterations of this remodelling.
How to program CPLD?
A logic design can be described using VHDL, a hardware description language (HDL). The VHDL logic design can then be read by software tools, which create a configuration file that can be loaded into a CPLD or FPGA to implement the logic design. VHSIC Hardware Description Language is known as VHDL. Very High-Speed Integrated Circuit is the abbreviation for this.
VHDL is a vendor-neutral language that has been standardized by the Institute of Electrical and Electronics Engineers (IEEE). It is now both transportable and reusable. In contrast to
conventional computer programs, most statements in VHDL occur continuously (in parallel with one another), not sequentially. Verilog is another HDL alternative to VHDL that is standardized and vendor-independent.
CPLD vs FPGA
| CPLD Characteristics | FPGA Characteristics |
|---|---|
| CPLDs, such as the Lattice ispLSI series, Xilinx XC9500 series, Altera MAX7000S series, and Lattice (previously Vantis) Mach series, are devices that are structured in a product term structured fashion to generate a logical behaviour. | FPGAs, such as those in the SPARTAN series from Xilinx, the FLEX10K or ACEX1K series from Altera, etc., are devices that are structured using a look-up table mechanism to create the logic behavior. |
| While CPLD works better with structures that have a lot of product words and few flip-flops. | Rich flip-flop structures are better suited for FPGA. |
| The CPLD’s continuous wiring arrangement ensures that its timing delays are consistent and foreseeable. | The unpredictable nature of the FPGA’s latency is determined by its segmented wire arrangement. |
| The logic function of the CPLD is modified using a fixed connection circuit, and it is coded underneath the logic block. | FPGAs are programmed using logic gates, whereas modifying the wiring of internal wires is how they are programmed. |
| FPGA confidentiality is poor compared to CPLD confidentiality. | Compared to CPLDs, FPGAs are more integrated and feature more intricate wiring and logic implementations. |
| E2PROM or FASTFLASH technology is used to program CPLDs, making them simple to use and requiring no additional memory chip. | While it is necessary to apply complicated procedures to store the FPGA programming data in external memory. |
| While CPLDs have collective connections between logic blocks and are programmed at the logic block level. CPLDs are therefore more time predictable and faster than FPGAs. | FPGAs use dispersed interconnections between CLBs and are programmable at the gate level. |
| Programming on the programmer and programming in the system are two further divisions of CPLD. | FPGAs, such as those in the SPARTAN series from Xilinx, the FLEX10K or ACEX1K series from Altera, etc., are devices that are structured using a look-up table mechanism to create the logic behaviour. |
CPLD Structure
(1) Basic structure of EPM7128S device
The major components of the EPM7128S device are the programmable interconnect array (PIA), macro cell, logic array block (LAB), and I/O control block. Each macrocell in the multi-array matrix structure has a customizable flip-flop with an individually programmable clock, clock enable, clear, and reset operations, as well as a programmable array and a fixed array. The global bus and the Programmable Interconnect Array PIA are used to connect several LABs. For direct input and output channels, each LAB is additionally connected to the associated I/O control module.
(2) Macro Cell Structure of EPM7128S device
The EPM7128S’s macrocells can each be separately set up to operate using combinational or timing logic. The logic array, the product term selection matrix, and the programmable registers are the three primary components of the macrocell. According to the logic requirements, the programmable registers can be programmed to ignore and implement combinational logic. The associated programmable logic device development software will choose the most efficient register operation when utilized as registers in order to minimize the device resources required for the design.