EPROM's are non volatile. They accept binary coded information and are commonly used in microcomputer systems. It is fairly easy to store data in an EPROM, by means of a so-called EPROM programmer. They will retain their data or information for more than 10 years even at temperatures around 70degreeC.The number of read cycles is also unlimited. An EPROM can easily be cleared by exposing it to the ultra violet light and then reprogrammed if required.

EPROM's are manufactured using HMOs - technology, their input and outputs being TTL compatible. Nearly all the available ones are also pin compatible to standard Ross and CMGs - RAMS. The main rules to be mentioned before programming a chip are before inserting an EPROM always check the programming voltage at point PV adjust the power supply to set the correct value or to be regulated for the device to be programmed. Never insert or remove an EPROM with the programmer switched on.

Types of ROMs

EROM - (Read only Memory)- Factory written and cannot be changed at all.

PROM - (Programmable ROM)- can be programmed at the field can be written only once and cannot be rewritten.

EPROM - (Electrically erasable programmable ROM)- can be erased and rewritten. Erasing needs special operations and is not simple over writing as RAM.

UVEPROM - (Ultraviolet erasable PROM)- UVrays are used to erase the previous data stored in EPROM.

Static RAMS (S-RAM)

RAM or Random Access memories are intended for storing digital data in computer system. A single memory cell (for one data bit) is similar to a flip-flop. It can be set, cleared and read .Static Rams are currently available in NMOS, HMOS and CMOS technology.

In the quiescent state, the current consumption of CMOS Rams is in the order of micro amps, making them especially suitable for battery back up applications. In these lCs are easy to use require relatively low power and fast access. The memory organization can be 1 bit, 4 bit or 8 bit and so on. A byte - wide memory using 1 bit types will be require 8 ICs in parallel.

Dynamic RAM(D-RAM)

Dynamic RAMS are direct access memory elements binary data in computer system. Unlike their static counter parts which require four or six transistors to store one bit, dynamic RAMs need only one MOS transistor and a capacitor. Naturally this makes them cheaper. However the capacitor (Which is about pF) discharges early and thus data can be lost.

To counteract this stored data must be refreshed every few milliseconds. The total current drawn is less than with normal. Static ICS but more than static CMGs - RAMS. Ignored to make the IC suitable 16pin package the address bus is multiplexed. Dynamic have an internal array in the firm of nx1 bit (only I bit can 1w input at a time) so to store data 8 bits wide (1 byte) 8 dynamic -RAMs are needed.