China
Africa
Explore chapters and articles related to this topic
Digital Logic Families
Published in Jerry C. Whitaker, Microelectronics, 2018
There is no universally accepted dividing line between complex PLDs and FPGAs. Not only do architectures differ from manufacturer to manufacturer, the method of interconnect programming also differs. The term complex programmable logic device (CPLD) generally denotes devices organized as large arrays of PAL macrocells, with fixed delay feedback of macrocells outputs into the AND–OR array (Fig. 7.16). CLPD time delays are more predictable than those of FPGAs, which can make them simpler to design with. A more important distinction between CPLDs and FPGAs is the ratio of combinatorial logic to sequential logic in their logic cells. The PAL-like structure of CPLDs means that the flip-flop in each logic macrocell is fed by the logical sum of several logical products. The products can include a large number of input and feedback signals. Thus, CPLDs are well suited to applications such as state machines that have logic functions including many variables. FPGAs, on the other hand, tend toward cells that include a flip-flop driven by a logic function of only three or so variables and are better suited to situations requiring many registers fed by relatively simple functions.
Advanced Digital Concepts
Published in Dale Patrick, Stephen Fardo, Vigyan ‘Vigs’ Chandra, Electronic Digital System Fundamentals, 2020
Dale Patrick, Stephen Fardo, Vigyan ‘Vigs’ Chandra
PLDs refer to the class of digital devices which have user-assigned logic functions. PLDs are available which contain both combinational and sequential logic features, making them suitable for a wide range of applications having low power, size and high-speed requirements. Early versions of PLDs included Programmable Array Logic (PAL) devices which contained a PROM array, implementing a sum-of-products, and output logic. The PALASM (PAL Assembler) design software was used for converting Boolean expressions into binary fuse patterns. These functioned similar to a lookup table based on the input applied to the device. Generic Array Logic (GAL) is a reprogrammable extension of PAL devices, thereby making them suitable for prototyping.
Semi-custom devices, programmable logic and device technology
Published in D.A. Bradley, N.C. Burd, D. Dawson, A.J. Loader, Mechatronics, 2018
D.A. Bradley, N.C. Burd, D. Dawson, A.J. Loader
The programmable array logic (PAL) chip is constructed from a programmable AND array to give flexibility in the programming of product terms, and a fixed output OR array to achieve a lower cost than the fully programmable PLA. The structure of the PAL is shown in Fig. 13.2c, where the fixed OR array can be seen to constrain the number of product terms available to an output variable. In the case shown in the figure, it can be seen that this is two product terms per output. PALs are therefore made available with a range of different output OR gate configurations which must be chosen to satisfy the logic function to be implemented.
All-optical programmable array logic unit using semiconductor optical amplifier-based polarization switch
Published in Journal of Modern Optics, 2022
Manas Kumar Garai, Mrinal Kanti Mandal, Sisir Kumar Garai
A programmable array logic (PAL) unit is a simple programmable logic device used to implement combinational logic circuits. A PAL has a programmable AND array committed to a particular OR gate, making the OR matrix fixed rather than programmable. To implement a particular function using PAL requires proper connections among the wires. The unwanted connections could be eliminated by fusing it; after programme design, the fuse is blown, protecting the PAL from being copied or further programmed. This feature makes it very beneficial for manufacturers to prevent illegal uses and decode the designed PAL matrix contents. In this system, only the programmed operations can be done, and not all others operations in one chip, i.e. the operations are dedicated only as it is programmed and no unauthorized person use the circuit chip. The AND-OR layout of a PAL allows to implement logic functions in the form of the sum of products.