Programmable logic device
A programmable logic device (PLD) is an electronic component used to build reconfigurable digital circuits.
[2] Unlike for microprocessors, programming a PLD changes the connections made between the gates in the device.
[3] In 1970, Texas Instruments developed a mask-programmable IC based on the IBM read-only associative memory or ROAM.
[5][6][7] In 1973 National Semiconductor introduced a mask-programmable PLA device (DM7575) with 14 inputs and 8 outputs with no memory registers.
[10] In 1970, Texas Instruments developed a mask-programmable IC based on the IBM read-only associative memory or ROAM.
The PALASM design software (PAL assembler) converted the engineers' Boolean equations into the fuse pattern required to program the part.
After buying out MMI (1987), AMD spun off a consolidated operation as Vantis, and that business was acquired by Lattice Semiconductor in 1999.
An improvement on the PAL was the generic array logic device, or GAL, invented by Lattice Semiconductor in 1985.
Lattice GALs combine CMOS and electrically erasable (E2) 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.
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.
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.
In general, CPLDs are a good choice for wide combinational logic applications, whereas FPGAs are more suitable for large state machines such as microprocessors.
Using the same technology as EPROMs, EPLDs have a quartz window in the package that allows them to be erased on exposure to UV light.
[15][16] 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.
Designing self-altering systems requires that engineers 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.
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.
The charge remains for many years and can only be removed by exposing the chip to strong ultraviolet light in a device called an EPROM eraser.
Flash memory is a kind of EEPROM that holds information using trapped electric charges similar to EPROM.
For modern PLD programming languages, design flows, and tools, see FPGA and reconfigurable computing.
