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  • Key Features of Field Programmable Gate Arrays (FPGAs)

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    John Mulindi
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    A field programmable gate array (FPGA) utilizes an array of logic blocks, which can be configured by the user. The term “field programmable” implies that the device is programmable outside the factory where it is produced. The internal architecture of a FPGA device has three main parts, namely: The figure below illustrates the architecture of…

  • Programmable Array Logic (PAL)

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    John Mulindi
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    Programmable array logic (PAL) architecture has a programmable AND array at the input and a fixed OR array at the output. The programmable AND array of a PAL device is similar to that of a programmable logic array (PLA) device. In other words, the number of programmable AND gates is usually smaller than the number…

  • Programmable Logic Array (PLA)

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    John Mulindi
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    A programmable logic array (PLA) device has a programmable AND array at the input and a programmable OR array at the output, which makes it one of the most versatile programmable logic devices. The figure below, shows the internal architecture of a PLA device with four input lines, a programmable array of eight AND gates…

  • Basic Structure of a Programmable ROM (PROM)

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    John Mulindi
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    The architecture of a programmable read only memory (PROM) allows the user to use the hardware in implementing an arbitrary combinational function of a given number of inputs. When utilized as a memory device, n inputs of the ROM (called address lines) and m outputs (called data lines) can be used to store 2nm-bit words.…

  • Choosing Between TTL & CMOS for Your Digital Logic Design

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    John Mulindi
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    There are two families of logic devices called TTL and CMOS. For those who are new to these devices, TTL stands for transistor transistor logic devices and CMOS for complementary metal-oxide semiconductor devices. Bipolar junction transistors are the building blocks for TTL logic, whereas MOSFETs are the building blocks for CMOS logic. Usually, any combinational…

  • Transistor Transistor Logic (TTL)

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    John Mulindi
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    Transistor transistor logic (TTL) is a logic family implemented with bipolar process technology that combines or integrates NPN transistors, PN junction diodes and diffused resistors in a single monolithic structure to get the desired logic function. The NAND gate is the basic building block of this logic family. We have different subfamilies in this logic…

  • Programmable Logic Device (PLD)

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    John Mulindi
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    Besides memory devices and microprocessors, logic devices make up one of the essential classes of devices utilized in digital computing systems. Memory devices like ROM & RAM are used for information storage such as software instructions of a program, or the contents of a database and microprocessors execute software instructions to perform a variety of…

  • 3 Categories of Digital Logic Families

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    John Mulindi
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    Digital ICs are usually fabricated using either bipolar devices or MOS devices or a combination of the two. We can classify the logic families into the following categories based on whether they are manufactured using bipolar, MOS or a combination of the two: Bipolar Families The families in this category include: diode logic (DL), resistor…

  • Data Registers

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    John Mulindi
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    Data registers are used in microcomputers to hold data temporarily. Normally this data can be accessed faster than if it were to be fetched from the memory. The figure below shows a 4-bit data register that utilizes a negative edge-triggered D flip-flops to transfer data from four data lines to the outputs of four AND…

  • Flip-Flops in Digital Circuits

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    John Mulindi
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    Since digital data is usually stored in the form bits, digital memory devices such as the computer random access memory (RAM) requires a way for storing and switching between the two binary states. A flip-flop is a sequential logic device that can perform this operation. The flip-flop is called a bistable device, because it has…