![Programmable Logic Device](https://upload.wikimedia.org/wikipedia/commons/f/f0/Programmable_Logic_Device.svg)
A programmable logic device (PLD) is an
electronic
Electronic may refer to:
*Electronics, the science of how to control electric energy in semiconductor
* ''Electronics'' (magazine), a defunct American trade journal
*Electronic storage, the storage of data using an electronic device
*Electronic co ...
component used to build
reconfigurable digital circuits
Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. This is in contrast to analog electronics and analog signals.
Digital electronic circuits are usually ...
. Unlike digital logic constructed using discrete
logic gate
A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, ...
s with fixed functions, a PLD has an undefined function at the
time of manufacture. Before the PLD can be used in a circuit it must be programmed to implement the desired function.
Compared to fixed logic devices, programmable logic devices simplify the design of complex logic and may offer superior performance. Unlike for
microprocessors
A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
, programming a PLD changes the connections made between the gates in the device.
PLDs can broadly be categorised into, in increasing order of complexity,
Simple Programmable Logic Devices (SPLDs), comprising
programmable array logic
Programmable Array Logic (PAL) is a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. (MMI) in March 1978. Introductory advertisement on PAL (Progra ...
,
programmable logic array and
generic array logic
The Generic Array Logic (also known as GAL and sometimes as gate array logic) device was an innovation of the PAL and was invented by Lattice Semiconductor. The GAL was an improvement on the PAL because one device type was able to take the place ...
;
Complex Programmable Logic Devices (CPLDs) and
Field-Programmable Gate Arrays (FPGAs).
History
In 1969,
Motorola
Motorola, Inc. () was an American Multinational corporation, multinational telecommunications company based in Schaumburg, Illinois, United States. After having lost $4.3 billion from 2007 to 2009, the company split into two independent p ...
offered the XC157, a mask-programmed gate array with 12 gates and 30 uncommitted input/output pins.
In 1970,
Texas Instruments
Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...
developed a mask-programmable IC based on the
IBM read-only associative memory or ROAM. This device, the TMS2000, was programmed by altering the metal layer during the production of the IC. The TMS2000 had up to 17 inputs and 18 outputs with 8
JK flip flop
In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information – a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs an ...
for memory. TI coined the term
Programmable Logic Array (PLA) for this device.
[ Report introduces the TMS2000 and TMS2200 series of mask programmable PLAs.]
In 1971,
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
Company (GE) was developing a programmable logic device based on the new
Programmable Read-Only Memory
A programmable read-only memory (PROM) is a form of digital memory where the contents can be changed once after manufacture of the device. The data is then permanent and cannot be changed. It is one type of read-only memory (ROM). PROMs are used ...
(PROM) technology. This experimental device improved on IBM's ROAM by allowing multilevel logic. Intel had just introduced the floating-gate
UV erasable PROM so the researcher at GE incorporated that technology. The GE device was the first erasable PLD ever developed, predating the
Altera
Altera Corporation was a manufacturer of programmable logic devices (PLDs) headquartered in San Jose, California. It was founded in 1983 and acquired by Intel in 2015.
The main product lines from Altera were the flagship Stratix series, mid-ran ...
EPLD by over a decade. GE obtained several early patents on programmable logic devices.
[Greer, David L. ''Electrically Programmable Logic Circuits']
US Patent 3,818,452
Assignee: General Electric, Filed: April 28, 1972, Granted: June 18, 1974[Greer, David L. ''Multiple Level Associative Logic Circuits']
US Patent 3,816,725
Assignee: General Electric, Filed: April 28, 1972, Granted: June 11, 1974[Greer, David L. ''Segmented Associative Logic Circuits']
US Patent 3,849,638
Assignee: General Electric, Filed: July 18, 1973, Granted: November 19, 1974
In 1973
National Semiconductor
National Semiconductor was an American semiconductor manufacturer which specialized in analog devices and subsystems, formerly with headquarters in Santa Clara, California. The company produced power management integrated circuits, display dr ...
introduced a mask-programmable PLA device (DM7575) with 14 inputs and 8 outputs with no memory registers. This was more popular than the TI part but cost of making the metal mask limited its use. The device is significant because it was the basis for the field programmable logic array produced by
Signetics
Signetics Corporation was an American electronics manufacturer specifically established to make integrated circuits. Founded in 1961, they went on to develop a number of early microprocessors and support chips, as well as the widely used 555 time ...
in 1975, the 82S100. (
Intersil
Intersil is an American semiconductor company headquartered in Milpitas, California. As of February 24, 2017, Intersil is a subsidiary of Renesas. The previous Intersil was formed in August 1999 through the acquisition of the semiconductor busin ...
actually beat Signetics to market but poor yield doomed their part.)
[ Press release on Intersil IM5200 field programmable logic array. Fourteen inputs pins and 48 product terms. Avalanched-induced-migration programming. Unit price was $37.50][ Press release on Signetics 82S100 and 82S101 field programmable logic arrays. Fourteen inputs pins, 8 output pins and 48 product terms. NiCr fuse link programming.]
In 1974 GE entered into an agreement with
Monolithic Memories
Monolithic Memories, Inc. (MMI) produced bipolar junction transistor, bipolar PROMs, programmable logic devices, and logic circuits (including 7400 series, 7400 series TTL).
A team of MMI engineers, under the direction of Ze'ev Drori and headed ...
(MMI) to develop a mask–programmable logic device incorporating the GE innovations. The device was named the 'Programmable Associative Logic Array' or PALA. The MMI 5760 was completed in 1976 and could implement multilevel or sequential circuits of over 100 gates. The device was supported by a GE design environment where Boolean equations would be converted to mask patterns for configuring the device. The part was never brought to market.
PLA
In 1970,
Texas Instruments
Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...
developed a mask-programmable IC based on the
IBM read-only associative memory or ROAM. This device, the TMS2000, was programmed by altering the metal layer during the production of the IC. The TMS2000 had up to 17 inputs and 18 outputs with 8
JK flip-flops
In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information – a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and w ...
for memory. TI coined the term
programmable logic array for this device.
A programmable logic array (PLA) has a programmable AND gate array, which links to a programmable OR gate array, which can then be conditionally complemented to produce an output. A PLA is similar to a ROM concept, however a PLA does not provide full decoding of a variable and does not generate all the
minterms as in a ROM.
PAL
PAL devices have arrays of transistor cells arranged in a "fixed-OR, programmable-AND" plane used to implement "sum-of-products" binary logic equations for each of the outputs in terms of the inputs and either synchronous or asynchronous feedback from the outputs.
MMI introduced a breakthrough device in 1978, the
programmable array logic
Programmable Array Logic (PAL) is a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. (MMI) in March 1978. Introductory advertisement on PAL (Progra ...
or PAL. The architecture was simpler than that of Signetics FPLA because it omitted the programmable OR array. This made the parts faster, smaller and cheaper. They were available in 20 pin 300 mil DIP packages while the FPLAs came in 28 pin 600 mil packages. The PAL Handbook demystified the design process. The PALASM design software (PAL assembler) converted the engineers' Boolean equations into the fuse pattern required to program the part. The PAL devices were soon
second-sourced by National Semiconductor, Texas Instruments and AMD.
After MMI succeeded with the 20-pin PAL parts,
AMD
Advanced Micro Devices, Inc. (AMD) is an American multinational semiconductor company based in Santa Clara, California, that develops computer processors and related technologies for business and consumer markets. While it initially manufactur ...
introduced the 24-pin
22V10 PAL with additional features. After buying out MMI (1987), AMD spun off a consolidated operation as
Vantis
Vantis plc was an accountancy firm based in London, England, providing accounting, tax and business advice to owner-managed businesses, listed companies, not for profit organisations, high-net-worth individuals and other professionals. It was pla ...
, and that business was acquired by
Lattice Semiconductor
Lattice Semiconductor Corporation is an American semiconductor company specializing in the design and manufacturing of low power, field-programmable gate arrays (FPGAs). Headquartered in the Silicon Forest area of Hillsboro, Oregon, the company ...
in 1999.
GALs
An improvement on the PAL was the generic array logic device, or GAL, invented by
Lattice Semiconductor
Lattice Semiconductor Corporation is an American semiconductor company specializing in the design and manufacturing of low power, field-programmable gate arrays (FPGAs). Headquartered in the Silicon Forest area of Hillsboro, Oregon, the company ...
in 1985. This device has the same logical properties as the PAL but can be erased and reprogrammed. The GAL is very useful in the prototyping stage of a design, when any
bugs in the logic can be corrected by reprogramming. GALs are programmed and reprogrammed using a PAL programmer, or by using the
in-circuit programming
In-system programming (ISP), or also called in-circuit serial programming (ICSP), is the ability of some programmable logic devices, microcontrollers, and other embedded devices to be programmed while installed in a complete system, rather th ...
technique on supporting chips.
Lattice GALs combine
CMOS
Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSFE ...
and electrically erasable (E
2) floating gate technology for a high-speed, low-power logic device. A similar device called a PEEL (programmable electrically erasable logic) was introduced by the International CMOS Technology (ICT) corporation.
CPLDs
PALs and GALs are available only in small sizes, equivalent to a few hundred logic gates. For bigger logic circuits, complex PLDs or
CPLDs can be used. These contain the equivalent of several PALs linked by programmable interconnections, all in one
integrated circuit
An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...
. CPLDs can replace thousands, or even hundreds of thousands, of logic gates.
Some CPLDs are programmed using a PAL programmer, but this method becomes inconvenient for devices with hundreds of pins. A second method of programming is to solder the device to its printed circuit board, then feed it with a serial data stream from a personal computer. The CPLD contains a circuit that decodes the data stream and configures the CPLD to perform its specified logic function. Some manufacturers (including
Altera
Altera Corporation was a manufacturer of programmable logic devices (PLDs) headquartered in San Jose, California. It was founded in 1983 and acquired by Intel in 2015.
The main product lines from Altera were the flagship Stratix series, mid-ran ...
and
Microsemi
Microsemi Corporation was an Aliso Viejo, California-based provider of semiconductor and system solutions for aerospace & defense, communications, data center and industrial markets.
In February 2018, it was announced that Chandler, Arizona-bas ...
) use
JTAG
JTAG (named after the Joint Test Action Group which codified it) is an Technical standard, industry standard for verifying designs and testing printed circuit boards after manufacture.
JTAG implements standards for on-chip instrumentation in ele ...
to program CPLDs in-circuit from
.JAM
JAM / STAPL ("Standard Test and Programming Language") is an Altera-developed standard for JTAG in-circuit programming of programmable logic devices which is defined by JEDEC standard JESD-71.
STAPL defines a standard ''.jam'' file format whic ...
files.
FPGAs
While PALs were being developed into GALs and CPLDs (all discussed above), a separate stream of development was happening. This type of device is based on
gate array
A gate array is an approach to the design and manufacture of application-specific integrated circuits (ASICs) using a prefabricated chip with components that are later interconnected into logic devices (e.g. NAND gates, flip-flops, etc.) according ...
technology and is called the
field-programmable gate array
A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware d ...
(FPGA). Early examples of FPGAs are the 82s100 array, and 82S105 sequencer, by Signetics, introduced in the late 1970s. The 82S100 was an array of AND terms. The 82S105 also had flip flop functions.
(Remark: 82S100 and similar ICs from Signetics have PLA-Structure, AND-Plane + OR-Plane)
FPGAs use a grid of
logic gate
A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, ...
s, and once stored, the data doesn't change, similar to that of an ordinary gate array. The term "field-programmable" means the device is programmed by the customer, not the manufacturer.
FPGAs are usually programmed after being soldered down to the circuit board, in a manner similar to that of larger CPLDs. In most larger FPGAs, the configuration is volatile and must be re-loaded into the device whenever power is applied or different functionality is required. Configuration is typically stored in a configuration
PROM
A promenade dance, commonly called a prom, is a dance party for high school students. It may be offered in semi-formal black tie or informal suit for boys, and evening gowns for girls. This event is typically held near the end of the school yea ...
or
EEPROM
EEPROM (also called E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a ...
. EEPROM versions may be in-system programmable (typically via
JTAG
JTAG (named after the Joint Test Action Group which codified it) is an Technical standard, industry standard for verifying designs and testing printed circuit boards after manufacture.
JTAG implements standards for on-chip instrumentation in ele ...
).
The difference between FPGAs and CPLDs is that FPGAs are internally based on
look-up tables (LUTs) whereas CPLDs form the logic functions with sea-of-gates (e.g.
sum of products). CPLDs are meant for simpler designs while FPGAs are meant for more complex designs. In general, CPLDs are a good choice for wide
combinational logic
In automata theory, combinational logic (also referred to as time-independent logic or combinatorial logic) is a type of digital logic which is implemented by Boolean circuits, where the output is a pure function of the present input only. This i ...
applications, whereas FPGAs are more suitable for large
state machine
A finite-state machine (FSM) or finite-state automaton (FSA, plural: ''automata''), finite automaton, or simply a state machine, is a mathematical model of computation. It is an abstract machine that can be in exactly one of a finite number o ...
s such as
microprocessors
A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
.
EPLDs
![PLCC84 UV Cypress](https://upload.wikimedia.org/wikipedia/commons/3/3c/PLCC84_UV_Cypress.jpg)
Using the same technology as
EPROM
An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power s ...
s, EPLDs have a quartz window in the package that allows it to be erased on exposure to UV light.
Using the same technology as
EEPROM
EEPROM (also called E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a ...
s, EEPLDs can be erased electrically.
[
Tertulien Ndjountche]
"Digital Electronics 2: Sequential and Arithmetic Logic Circuits"
2016.
p. 224.
[
Clive Maxfield]
"The Design Warrior's Guide to FPGAs"
2004.
p. 20
An Erasable programmable logic device (EPLD) is an integrated circuit that comprises an array of PLDs that do not come pre-connected; the connections are programmed electrically by the user. Most GAL and FPGA devices are examples of EPLDs.
Other variants
These are microprocessor circuits that contain some
fixed functions and other functions that can be altered by code running on the processor. Designing self-altering systems requires engineers to learn new methods, and that new software tools be developed.
PLDs are being sold now that contain a microprocessor with a fixed function (the so-called ''core'') surrounded by programmable logic. These devices let designers concentrate on adding new features to designs without having to worry about making the microprocessor work. Also, the fixed-function microprocessor takes less space on the chip than a part of the programmable gate array implementing the same processor, leaving more space for the programmable gate array to contain the designer's specialized circuits.
How PLDs retain their configuration
A PLD is a combination of a logic device and a
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
device. The memory is used to store the pattern that was given to the chip during programming. Most of the methods for storing data in an integrated circuit have been adapted for use in PLDs. These include:
*
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
antifuse
An antifuse is an electrical device that performs the opposite function to a fuse. Whereas a fuse starts with a low resistance and is designed to permanently break an electrically conductive path (typically when the current through the path exceeds ...
s
*
SRAM
*
EPROM
An EPROM (rarely EROM), or erasable programmable read-only memory, is a type of programmable read-only memory (PROM) chip that retains its data when its power supply is switched off. Computer memory that can retrieve stored data after a power s ...
or
EEPROM
EEPROM (also called E2PROM) stands for electrically erasable programmable read-only memory and is a type of non-volatile memory used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a ...
memory cells
*
Flash memory
Flash memory is an electronic non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR and NAND logic gates. Both us ...
Silicon antifuses are connections that are made by applying a voltage across a modified area of silicon inside the chip. They are called antifuses because they work in the opposite way to normal fuses, which begin life as connections until they are broken by an electric current.
SRAM, or static RAM, is a volatile type of memory, meaning that its contents are lost each time the power is switched off. SRAM-based PLDs therefore have to be programmed every time the circuit is switched on. This is usually done automatically by another part of the circuit.
An EPROM memory cell is a
MOSFET
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
(metal-oxide semiconductor field-effect transistor, or MOS transistor) that can be switched on by trapping an electric charge permanently on its gate electrode. This is done by a PAL programmer. The charge remains for many years and can only be removed by exposing the chip to strong
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
light in a device called an EPROM eraser.
Flash memory is non-volatile, retaining its contents even when the power is switched off. It is stored on
floating-gate MOSFET
The floating-gate MOSFET (FGMOS), also known as a floating-gate MOS transistor or floating-gate transistor, is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) where the gate is electrically isolated, creating a floating no ...
memory cells, and can be erased and reprogrammed as required. This makes it useful in PLDs that may be reprogrammed frequently, such as PLDs used in prototypes. Flash memory is a kind of EEPROM that holds information using trapped electric charges similar to EPROM. Consequently, Flash memory can hold information for years, but possibly not as many years as EPROM.
As of 2005, most CPLDs are electrically programmable and erasable, and non-volatile. This is because they are too small to justify the inconvenience of programming internal SRAM cells every time they start up, and EPROM cells are more expensive due to their ceramic package with a quartz window.
PLD programming languages
Many PAL programming devices accept input in a standard file format, commonly referred to as '
JEDEC
The JEDEC Solid State Technology Association is an independent semiconductor engineering trade organization and standardization body headquartered in Arlington County, Virginia, United States.
JEDEC has over 300 members, including some of the w ...
files'. They are analogous to
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
compiler
In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs that ...
s. The languages used as source code for logic compilers are called
hardware description language
In computer engineering, a hardware description language (HDL) is a specialized computer language used to describe the structure and behavior of electronic circuits, and most commonly, digital logic circuits.
A hardware description language e ...
s, or HDLs.
PALASM
PALASM is an early hardware description language, used to translate Boolean functions and state transition tables into a fuse map for use with Programmable Array Logic (PAL) devices introduced by Monolithic Memories, Inc. (MMI). The language was d ...
,
ABEL
Abel ''Hábel''; ar, هابيل, Hābīl is a Biblical figure in the Book of Genesis within Abrahamic religions. He was the younger brother of Cain, and the younger son of Adam and Eve, the first couple in Biblical history. He was a shepherd ...
and
CUPL are frequently used for low-complexity devices, while
Verilog
Verilog, standardized as IEEE 1364, is a hardware description language (HDL) used to model electronic systems. It is most commonly used in the design and verification of digital circuits at the register-transfer level of abstraction. It is als ...
and
VHDL
The VHSIC Hardware Description Language (VHDL) is a hardware description language (HDL) that can model the behavior and structure of digital systems at multiple levels of abstraction, ranging from the system level down to that of logic gates ...
are popular higher-level description languages for more complex devices. The more limited ABEL is often used for historical reasons, but for new designs VHDL is more popular, even for low-complexity designs.
For modern PLD programming languages, design flows, and tools, see
FPGA
A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware de ...
and
Reconfigurable computing
Reconfigurable computing is a computer architecture combining some of the flexibility of software with the high performance of hardware by processing with very flexible high speed computing fabrics like field-programmable gate arrays (FPGAs). Th ...
.
PLD programming devices
A
device programmer
This glossary of computer hardware terms is a list of definitions of terms and concepts related to computer hardware, i.e. the physical and structural components of computers, architectural issues, and peripheral devices.
A
...
is used to transfer the boolean logic pattern into the programmable device. In the early days of programmable logic, every PLD manufacturer also produced a specialized device programmer for its family of logic devices. Later, universal device programmers came onto the market that supported several logic device families from different manufacturers. Today's device programmers usually can program common PLDs (mostly PAL/GAL equivalents) from all existing manufacturers. Common file formats used to store the boolean logic pattern (fuses) are JEDEC, Altera POF (programmable object file), or Xilinx BITstream.
PLD File Formats
/ref>
See also
* Complex programmable logic device (CPLD)
* Field-programmable gate array
A field-programmable gate array (FPGA) is an integrated circuit designed to be configured by a customer or a designer after manufacturinghence the term '' field-programmable''. The FPGA configuration is generally specified using a hardware d ...
(FPGA)
* Macrocell array
Macrocell arrays in PLDs
Programmable logic devices, such as programmable array logic and complex programmable logic devices, typically have a macrocell on every output pin.
Macrocell arrays in ASICs
A macrocell array is an approach to t ...
* Programmable array logic
Programmable Array Logic (PAL) is a family of programmable logic device semiconductors used to implement logic functions in digital circuits introduced by Monolithic Memories, Inc. (MMI) in March 1978. Introductory advertisement on PAL (Progra ...
(PAL)
References
External links
*
*
{{DEFAULTSORT:Programmable Logic Device
Gate arrays