Programmable Array Logic

Programmable Array Logic: We have seen that  PLA device with a Programmable AND array and Programmable OR array. However, Programmable Array Logic programmable logic device with a fixed OR array and a programmable AND array. Because only AND gates are programmable , the PAL is easier to program, but is not as flexible as the PLA. Fig.3.106 […]

Programmable Logic Array

Programmable Logic Array (PLA): Programmable Logic Array – The combinational circuit do not use all the minterms every time. Occasionally, they have don’t care conditions. Don’t care condition when implemented with a ROM becomes an address input that will never occur. The result is that not all the bit patterns available in the ROM are […]

Read Only Memory

Read Only Memory (ROM): A Read Only Memory (ROM) is a device that includes both the decoder and the OR gates within a single IC package. The Fig. 3.82 shows the block diagram of ROM. It consists of n input lines and m output lines. Each bit combination of the input variables is called an […]

Array Structures

Design of Array Structures: We have seen the design of digital circuits using fixed function ICs. There are two more approaches for the Design of Array Structures. Use of application specific integrated circuits (ASICs) Use of programmable logic devices (PLDs) In the fixed function IC approach, we have to use various fixed function ICs to […]

Dynamic RAM

Dynamic RAM: Dynamic RAM stores the data as a charge on the capacitor. Fig.3.77 shows the dynamic RAM cell. A dynamic RAM contains thousands of such memory cells. When COLUMN (Sence) and ROW (Control) lines go high, the MOSFET conducts and charges the capacitor. When the COLUMN and ROW lines go low, the MOSFET opens […]

RAM and its Architecture

RAM and its Architecture: RAM and its Architecture – Unlike ROM, we can read from or write into the RAM, so it is often called read/write memory. The numerical and character data that are to be processed by the computer change frequently. These data must be stored in type of memory from which they can […]

Flash Memory

Flash Memory: Flash memory (sometimes called “flash RAM”) is a type of constantly-powered nonvolatile memory that can be erased and reprogrammed in units of memory called blocks. It is a variation of electrically erasable programmable read-only memory (EEPROM) which, unlike flash memory, is erased and rewritten at the byte level, which is slower than flash […]

Electrically Erasable Programmable Read Only Memory

Electrically Erasable Programmable Read Only Memory: Electrically Erasable Programmable Read Only Memory also use MOS circuitry very similar to that of EPROM. Data is stored as charge or no charge on an insulated layer or an insulated floating gate in the device. The insulating layer is made very thin {< 200 A} Therefore, a voltage as […]

Erasable Programmable Read Only Memory

Erasable Programmable Read Only Memory: Erasable Programmable Read Only Memory use MOS circuitry. They store 1s and Os as a packet of charge in a buried layer of the IC chip. EPROMs can be programmed by the user with a special EPROM programmer. The important point is that we can erase the stored data in the […]

Design of Memory

Design of Memory: Design of Memory – Memories are made up of registers. Each register in the memory is one storage location. Each location is identified by an address. The number of storage locations can vary from a few in some memories to hundreds of thousand in others. Each location can accommodate one or more […]

Mealy Circuit

Mealy Circuit: When the output of the sequential circuit depends on both the present state of flip-flop(s) and on the input(s), the sequential circuit is referred to as Mealy circuit. Fig. 3.39 shows the sample Mealy circuits. As shown in the Fig. 3.39, the output of the circuit is derived from the combination of present […]

Moore Circuit

Moore Circuit: As mentioned earlier, when the output of the sequential circuit depends only on the present state of the flip-flop, the sequential circuit is referred to as Moore Circuit. Let us see one example of Moore circuits. Fig. 3.37 shows a sequential circuit which consists of two JK flip-flops and AND gate. The circuit […]