Programmable Array Logic - AbsoluteAstronomy.com

The term Programmable Array Logic (PAL) is used to describe a family of programmable logic device

Programmable logic device

A programmable logic device or PLD is an electronic component used to build reconfigurable digital circuits. Unlike a logic gate, which has a fixed function, a PLD has an undefined function at the time of manufacture...

semiconductors used to implement logic

Logic

In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...

functions in digital circuits

Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...

introduced by Monolithic Memories

Monolithic Memories

Monolithic Memories, Inc. produced bipolar PROMs, programmable logic devices, and logic circuits .A team of MMI engineers,under the direction of Ze'ev Drori and headed by John Birkner and H. T...

, Inc. (MMI) in March 1978. MMI obtained a registered trademark on the term PAL for use in "Programmable Semiconductor Logic Circuits". The trademark is currently held by Lattice Semiconductor

Lattice Semiconductor

Lattice Semiconductor Corporation is a United States based manufacturer of high-performance programmable logic devices . Founded in 1983, the company employs about 700 people and has annual revenues of around $300 million, with Darin Billerbeck as the chief executive officer...

.

PAL devices consisted of a small PROM (programmable read-only memory) core and additional output logic used to implement particular desired logic functions with few components.

Using specialized machines, PAL devices were "field-programmable". Each PAL device was "one-time programmable" (OTP), meaning that it could not be updated and reused after its initial programming. (MMI also offered a similar family called HAL, or "hard array logic", which were like PAL devices except that they were mask-programmed at the factory.)

Early history

Before PALs were introduced, designers of digital logic circuits would use small-scale integration (SSI) components, such as those in the 7400 series

7400 series

The 7400 series of transistor-transistor logic integrated circuits are historically important as the first widespread family of TTL integrated circuit logic. It was used to build the mini and mainframe computers of the 1960s and 1970s...

TTL (transistor-transistor logic

Transistor-transistor logic

Transistor–transistor logic is a class of digital circuits built from bipolar junction transistors and resistors. It is called transistor–transistor logic because both the logic gating function and the amplifying function are performed by transistors .TTL is notable for being a widespread...

) family; the 7400 family included a variety of logic building blocks, such as gates (NOT, NAND

NAND gate

The Negated AND, NO AND or NAND gate is the opposite of the digital AND gate, and behaves in a manner that corresponds to the opposite of AND gate, as shown in the truth table on the right. A LOW output results only if both the inputs to the gate are HIGH...

, NOR

NOR gate

The NOR gate is a digital logic gate that implements logical NOR - it behaves according to the truth table to the right. A HIGH output results if both the inputs to the gate are LOW . If one or both input is HIGH , a LOW output results. NOR is the result of the negation of the OR operator...

, AND

AND gate

The AND gate is a basic digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output results only if both the inputs to the AND gate are HIGH . If neither or only one input to the AND gate is HIGH, a LOW output results...

, OR

OR gate

The OR gate is a digital logic gate that implements logical disjunction - it behaves according to the truth table to the right. A HIGH output results if one or both the inputs to the gate are HIGH . If neither input is HIGH, a LOW output results...

), multiplexers (MUXes) and demultiplexers (DEMUXes), flip flops

Flip-flop (electronics)

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic...

(D-type, JK, etc.) and others. One PAL device would typically replace dozens of such "discrete" logic packages, so the SSI business went into decline as the PAL business took off. PALs were used advantageously in many products, such as minicomputers, as documented in Tracy Kidder

Tracy Kidder

John Tracy Kidder is a Pulitzer Prize-winning American writer of the 1981 nonfiction narrative, The Soul of a New Machine, about the creation of a new computer at Data General Corporation...

's best-selling book "The Soul of a New Machine

The Soul of a New Machine

Tracy Kidder's non-fiction book, The Soul of a New Machine, chronicles the experiences of an engineering team racing to design a next generation computer under a blistering schedule and tremendous pressure. This machine was eventually launched in 1980 as the Data General Eclipse MV/8000...

."

PALs were not the first commercial programmable logic devices; Signetics

Signetics

Signetics, once a major player in semiconductor manufacturing, made a variety of devices which included integrated circuits, bipolar and MOS, the Dolby circuit, logic, memory and analog circuits. They developed microprocessors like the 2650, the bipolar 8X300 and had licensed Motorola 68000...

had been selling its field programmable logic array (FPLA) since 1975. These devices were completely unfamiliar to most circuit designers and were perceived to be too difficult to use. The FPLA had a relatively slow maximum operating speed (due to having both programmable-AND and programmable-OR arrays), was expensive, and had a poor reputation for testability. Another factor limiting the acceptance of the FPLA was the large package, a 600-mil

Thou (unit of length)

A thou also known as a mil or point, is the verbalized abbreviation for "thousandth of an inch." It is a unit of length equal to 0.001 inch....

(0.6", or 15.24 mm) wide 28-pin dual in-line package

Dual in-line package

In microelectronics, a dual in-line package is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board or inserted in a socket.A DIP is usually referred to as a DIPn, where n is...

(DIP).

The project to create the PAL device was managed by John Birkner and the actual PAL circuit was designed by H. T. Chua. In a previous job, Birkner had developed a 16-bit processor using 80 standard logic devices. His experience with standard logic led him to believe that user programmable devices would be more attractive to users if the devices were designed to replace standard logic. This meant that the package sizes had to be more typical of the existing devices, and the speeds had to be improved. The PAL met these requirements and was a huge success and were "second source

Second source

In the electronics industry, a second source is a company that is licensed to manufacture and sell components originally designed by another company ....

d" by National Semiconductor

National Semiconductor

National Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...

, Texas Instruments

Texas Instruments

Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...

, and Advanced Micro Devices

Advanced Micro Devices

Advanced Micro Devices, Inc. or AMD is an American multinational semiconductor company based in Sunnyvale, California, that develops computer processors and related technologies for commercial and consumer markets...

Process technologies

Early PALs were 20-pin DIP

Dual in-line package

components fabricated in silicon using bipolar transistor technology with one-time programmable (OTP) titanium-tungsten programming fuses. Later devices were manufactured by Lattice Semiconductor

Lattice Semiconductor

and Advanced Micro Devices

Advanced Micro Devices

using CMOS

CMOS

Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...

technology.

The original 20 and 24-pin PALs were described by MMI as medium-scale integration (MSI) devices.

PAL architecture

The PAL architecture consists of two main components: a logic plane and output logic macrocells.

Programmable logic plane

The programmable logic plane is a programmable read-only memory

Programmable read-only memory

A programmable read-only memory or field programmable read-only memory or one-time programmable non-volatile memory is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently...

(PROM) array that allows the signals present on the devices pins (or the logical complements of those signals) to be routed to an output logic macrocell.

PAL devices have arrays of transistor cells arranged in a "fixed-OR, programmable-AND" plane used to implement "sum-of-products

Disjunctive normal form

In boolean logic, a disjunctive normal form is a standardization of a logical formula which is a disjunction of conjunctive clauses. As a normal form, it is useful in automated theorem proving. A logical formula is considered to be in DNF if and only if it is a disjunction of one or more...

" binary logic equations for each of the outputs in terms of the inputs and either synchronous or asynchronous feedback from the outputs.

Output logic

The early 20-pin PALs had 10 inputs and 8 outputs. The outputs were active low and could be registered or combinational. Members of the PAL family were available with various output structures called "output logic macrocells" or OLMCs. Prior to the introduction of the "V" (for "variable") series, the types of OLMCs available in each PAL were fixed at the time of manufacture. (The PAL16L8 had 8 combinational outputs and the PAL16R8 had 8 registered outputs. The PAL16R6 had 6 registered and 2 combinational while the PAL16R4 had 4 of each.) Each output could have up to 8 product terms (effectively AND gates), however the combinational outputs used one of the terms to control a bidirectional output buffer. There were other combinations that had fewer outputs with more product term per output and were available with active high outputs. The 16X8 family or registered devices had an XOR gate before the register. There were also similar 24-pin versions of these PALs.

This fixed output structure often frustrated designers attempting to optimize the utility of PAL devices because output structures of different types were often required by their applications. (For example, one could not get 5 registered outputs with 3 active high combinational outputs.) So, in June 1983 AMD introduced the 22V10, a 24 pin device with 10 output logic macrocells. Each macrocell could be configured by the user to be combinational or registered, active high or active low. The number of product term allocated to an output varied from 8 to 16. This one device could replace all of the 24 pin fixed function PAL devices. Members of the PAL "V" ("variable") series included the PAL16V8, PAL20V8 and PAL22V10.

Programming PALs

PALs were programmed electrically using binary patterns (as JEDEC

JEDEC

The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

/hexadecimal

Hexadecimal

In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...

files) and a special electronic programming system available from either the manufacturer or a third-party, such as DATA/IO

Data I/O Corporation

Data I/O Corporation is a manufacturer of programming and automated device handling systems for programmable integrated circuits. The company is headquartered in Redmond, Washington with sales and engineering offices worldwide.- History :...

. In addition to single-unit device programmers, device feeders and gang programmers were often used when more than just a few PALs needed to be programmed. (For large volumes, electrical programming costs could be eliminated by having the manufacturer fabricate a custom metal mask used to program the customers' patterns at the time of manufacture; MMI used the term "hard array logic" (HAL) to refer to devices programmed in this way.)

Programming languages

Though some engineers programmed PAL devices by manually editing files containing the binary fuse pattern data, most opted to design their logic using a hardware description language

Hardware description language

In electronics, a hardware description language or HDL is any language from a class of computer languages, specification languages, or modeling languages for formal description and design of electronic circuits, and most-commonly, digital logic...

(HDL) such as Data I/O's ABEL, Logical Devices' CUPL, or MMI's PALASM

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 devices introduced by Monolithic Memories, Inc. The language was developed by John Birkner in the early 1980s. It is not...

. These were computer-assisted design (CAD) (now referred to as "electronic design automation

Electronic design automation

Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...

") programs which translated (or "compiled") the designers' logic equations into binary fuse map files used to program (and often test) each device.

PALASM

The PALASM

PALASM

(from "PAL assembler") language was used to express boolean equations for the outputs pins in a text file which was then converted to the 'fuse map' file for the programming system using a vendor-supplied program; later the option of translation from schematics became common, and later still, 'fuse maps' could be 'synthesized' from an HDL

Hardware description language

(hardware description language,) such as Verilog

Verilog

In the semiconductor and electronic design industry, Verilog is a hardware description language used to model electronic systems. Verilog HDL, not to be confused with VHDL , is most commonly used in the design, verification, and implementation of digital logic chips at the register-transfer level...

.

The PALASM compiler was written by MMI in FORTRAN IV on an IBM 370/168. MMI made the source code available to users at no cost. By 1983, MMI customers ran versions on the DEC

Digital Equipment Corporation

Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

PDP-11

The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...

, Data General NOVA

Data General Nova

The Data General Nova was a popular 16-bit minicomputer built by the American company Data General starting in 1969. The Nova was packaged into a single rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world, and...

, Hewlett-Packard

Hewlett-Packard

Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...

HP2100, MDS800 and others.

CUPL

Logical Devices, Inc. released the Universal Compiler for Programmable Logic (CUPL), which ran under MSDOS on the IBM PC and is currently available as an integrated development package for Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

Device programmers

Popular device programmers included Data I/O Corporation

Data I/O Corporation

's Model 60A Logic Programmer and Model 2900.

One of the very first PAL Programmers was the Structured Design "SD-20". They had the PALASM software built-in and only required a CRT terminal to enter the equations and view the fuse plots. After fusing, the outputs of the PAL could be verified if test vectors were entered in the source file.

Successors

After MMI succeeded with the 20-pin PAL parts introduced circa 1978, AMD introduced the 24-pin 22V10 PAL with additional features. After buying out MMI (circa 1987), AMD spun off a consolidated operation as Vantis, and that business was acquired by Lattice Semiconductor

Lattice Semiconductor

in 1989.

Altera introduced the EP300 (first CMOS PAL) in 1983 and later moved into the FPGA business.

Lattice Semiconductor introduced the generic array logic

Generic array logic

The Generic 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 was able to take the place of many PAL devices or could even have functionality not covered by the original range...

(GAL

Generic array logic

) family in 1985, with functional equivalents of the "V" series PALs that used reprogrammable logic planes based on EEPROM

EEPROM

EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...

(electrically eraseable programmable read-only memory) technology. National Semiconductor was a "second source" of GAL parts. AMD introduced a similar family called PALCE. In general one GAL part is able to function as any of the similar family PAL devices. For example the 16V8 GAL is able to replace the 16L8, 16H8, 16H6, 16H4, 16H2 and 16R8 PALs (and many others besides).

ICT (International CMOS Technology) introduced the PEEL 18CV8 in 1986. The 20-pin CMOS EEPROM part could be used in place of any of the registered-output bipolar PALs and used much less power.

Larger-scale programmable logic devices were introduced by Atmel

Atmel

Atmel Corporation is a manufacturer of semiconductors, founded in 1984. Its focus is on system-level solutions built around flash microcontrollers...

, Lattice Semiconductor

Lattice Semiconductor

, and others. These devices extended the PAL architecture by including multiple logic planes and/or burying logic macrocells within the logic plane(s). The term "complex programmable logic device" (CPLD) was introduced to differentiate these devices from their PAL and GAL predecessors, which were then sometimes referred to as "simple programmable logic devices" or SPLDs.

Another large programmable logic device is the "field-programmable gate array

Field-programmable gate array

A field-programmable gate array is an integrated circuit designed to be configured by the customer or designer after manufacturing—hence "field-programmable"...

" or FPGA. This term is often used to describe devices currently made by Altera

Altera

Altera Corporation is a Silicon Valley manufacturer of PLDs . The company offered its first programmable logic device in 1984. PLDs can be reprogrammed during the design cycle as well as in the field to perform multiple functions, and they support a fairly fast design process...

and Xilinx

Xilinx

Xilinx, Inc. is a supplier of programmable logic devices. It is known for inventing the field programmable gate array and as the first semiconductor company with a fabless manufacturing model....

Early history

Process technologies

PAL architecture

Programmable logic plane

Output logic

Programming PALs

Programming languages

PALASM

CUPL

Device programmers

Successors

See also