PLD(programmable logic device)

PLD(programmable logic device) ：as a general PLD is integrated circuit production, his logic functions according to user to device programming to fix. General PLD integration high enough to satisfy the design general digital system needs. So you can from the designer by a digital system programming and "integrated" in a PLD, without having to go please chip manufacturer to design and manufacture special integrated circuit chips.

classification

Currently used PLD products mainly are: 1, field programmable logical array FPLA; 2, programmable logical array PAL, GAL 3, general array logic, 4, can erase programmable logic devices EPLD, 5 and the field reprogrammable array FPGA. One EPLD and FPGA integration is quite high. Sometimes make both device called high-density PLD.

Development course

Early programmable logic devices only programmable read-only CunZhuQi (PROM), ultraviolet ray can press except read-only CunZhuQi (an EPROM) and electricity can erase read-only CunZhuQi (EEPROM) 3 kinds. Due to the structure limits, they can only implement simple digital logic function.

Thereafter, the emergence of a class of structure slightly complex programmable chip, can programming logical device, it can finish all kinds of digital logic function. The typical PLD by an "and" door and a "or" gate arrays composed of any combinational logic can use "and a" expressions to describe or, so, with product and PLD can do a great deal of the form of combinational logic function. This one phase of products mainly include GAL PAL and. PAL by a programmable "and" plane and a fixed "or" planar formation, or through the gate outputs can be set to trigger selective hosting state. PAL devices are field programmable, its realization process has anti melt silk technology, an EPROM technology and EEPROM technology. And those structure is more flexible logic devices is programmable logical array (PLA), it can also by an "and" plane and a "or" plane composition, but the two plane connections is programmable. The plaaf device both field programmable, also have mask programmable. On the basis of PAL, and developed a GAL, such as general array logic GAL16V8, GAL22V10 etc. It adopted EEPROM process, realized the electricity can press except, electricity can rewrite, its output structure is programmable logic macro unit, so it has a strong design flexibility, so far, there are still many people use. These early PLD device of a common characteristic is can realize speed characteristics better logic functions, but its too simple structure also make they can only achieve smaller circuits. In order to make up for the defect, in 1980s and Altera Xilinx respectively introduced a similar to PAL structure of expandable CPLD and with standard gate array FPGA, they are similar with the system structure and logical unit that flexible, and integration is high and wide application scope, etc. These two kinds of devices compatible PLD and general gate arrays, can realize the advantages of large-scale circuit, programming is also very flexible. And the gate arrays, compared to other ASIC design and have them short development cycle, design and manufacture of low cost, development tools is advanced, the standard products without testing, stable quality and real-time on-line inspection etc, and therefore have been widely applied in product prototype design and product production (usually in 10,000 units under) among. Nearly all applications gate arrays, PLD and middle and small general digital integrated circuit occasions are applied FPGA and CPLD device.

composition

· a two-dimensional array logic brick, constitutes the core of the device consisting PLD logic.

· input/output block: connect logical pieces of interconnect resources.

· attachment resources: by all sorts of length of attachment, including hidden-lines composition have also some programmable connecting switch, they are used in logic brick, between the logic brick and input/output block the connection between the.