Introduction to Memory Devices - GATE ECE Engineering (ECE) Digital Circuits

The full form of ROM is Read Only Memory.

• ROM stands for Read Only Memory.
• It is a type of non-volatile storage used in computers and other devices.
• Data stored in ROM is not lost when the device is powered off.

For reprogrammability, PLDs use EPROM (i.e. Erasable PROM). It erases the previous program and starts uploading a new one. However, data is erased by exposing it to UV-light, which is a tedious and time-consuming process.

The full form of EPROM is Erasable Programmable Read Only Memory, where the ROM can be erased and re-used by the user.
 

When both the AND and OR are programmable, such PLDs are known as PLA (i.e. Programmable Logic Array). However, PLA is more flexible but has less speed.

The programmability and high density of PLDs make them useful in the design of ASIC (i.e. Application Specific Integrated Circuits) where design changes can be more rapidly and inexpensively.

The difference between FPGA and PLD is that FPGA incorporates logic blocks instead of fixed AND-OR gates and is faster with low power dissipation. FPGAs are designed for having higher gate count whereas, PLDs are used for lesser gate counts.

ROM consists of NAND and OR arrays which can be programmed by the user to implement combinational & sequential functions. Combinational Operations like that of adders and subtractors and Sequential Functions like that of storing in the memory.

The full form of PROM is Programmable Read Only Memory, where the ROM can be programmed by the user.

PLDs with programmable AND and fixed OR arrays are called PAL (i.e. Programmable Array Logic). However, PAL is less flexible but has higher speed.

In digital electronics, ASIC stands for Application Specific Integrated Circuits. It is a customized integrated circuit which is produced for a specific use and not for a common-purpose.