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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 (Programmable Array Logic).〕 MMI obtained a registered trademark on the term PAL for use in "Programmable Semiconductor Logic Circuits". The trademark is currently held by Lattice Semiconductor.〔Monolithic Memories, Inc (MMI) filed for a work mark on the term "PAL" for use in "Programmable Semiconductor Logic Circuits" on April 13, 1978. A registered trademark was granted on April 29, 1980, registration number 1134025. MMI's first use of the term PAL in commerce was on February 21, 1978. The trademark is currently held by Lattice Semiconductor Corporation of Hillsboro, Oregon. Source: United States Patent and Trademark Office online database.〕 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". PALs were available in several variants: * "One-time programmable" (OTP) devices could not be updated and reused after 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.). * UV erasable versions (e.g.: PALCxxxxx e.g.: PALC22V10) had a quartz window over the chip die and could be erased for re-use with an ultraviolet light source just like an EPROM. * Later versions (PALCExxx e.g.: PALCE22V10) were flash erasable devices. In most applications, electrically-erasable GALs are now deployed as pin-compatible direct replacements for one-time programmable PALs. ==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 TTL (transistor-transistor logic) family; the 7400 family included a variety of logic building blocks, such as gates (NOT, NAND, NOR, AND, OR), multiplexers (MUXes) and demultiplexers (DEMUXes), flip flops (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's best-selling book ''The Soul of a New Machine''. PALs were not the first commercial programmable logic devices; Signetics 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 (0.6", or 15.24 mm) wide 28-pin dual in-line package (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 (at mini-computer manufacturer Computer Automation), 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. MMI intended PALs to be a relatively low cost (sub $3) part. However, they initially had severe manufacturing yield problems and had to sell the devices for over $50. This threatened the viability of the PAL as a commercial product and they were forced to license the product line to National Semiconductor. PALs were later "second sourced" by Texas Instruments and Advanced Micro Devices. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Programmable Array Logic」の詳細全文を読む スポンサード リンク
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