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Combinational logic circuits
Published in David Crecraft, David Gorham, electronics, 2018
Large combinational logic problems can be solved by connecting many SSI and MSI devices together, but cheaper and smaller solutions can usually be found by using some form of programmable device. The term programmable in this context means that initially the devices have no specified logical function. You, as the user, define the function and then alter the device in some way so that it conforms to your specification. There are very many forms of programmable logic device (PLD), and these are generally divided into simple PLDs (SPLDs) and complex PLDs (CPLDs). This section will cover two types of SPLD,namely programmable array logic (PAL) devices and programmable readonly memory (PROM). As you will see, the PAL devices and PROM take very different approaches to the representation of combinational problems.
Computer System Organisation
Published in Pranabananda Chakraborty, Computer Organisation and Architecture, 2020
Generally, PLDs can be described as being one of three different types: simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), or field-programmable gate arrays (FPGAs). There are several manufacturers with many different families of PLDs, so there are many variations in the architecture. The distinction between CPLDs and FPGAs, however, is often fuzzy, with the manufacturers constantly designing new, improved architectures, and frequently muddying the water for their own marketing purposes. The CPLDs and FPGAs are thus often referred to collectively as high-capacity programmable logic devices (HCPLDs). The programming technologies being used for PLDs are actually based on the various types of available semiconductor memory. As more and more new types of enhanced memory with improved technology have been introduced, the same technology has been applied in the realization of new types of enhanced PLDs. To program PLDs, two techniques are commonly used, which are as follows: Mask programming, which requires a few special steps to be carried out in the fabricating process of IC chips containing PLDs;Field programming, which is carried out by the designers or end users in the field with the help of small, low-cost programming units. Some of these PLDs are erasable to allow the same IC to be reprogrammed many times. This feature is effectively exploited by the designers at the time of developing and debugging a prototype of a new product.
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.