EPROM (UV Erasable/OTP PROM)

EPROM (UV Erasable/OTP PROM)

An EPROM (erasable programmable-only memory) is a computer memory chip that can only be erased by exposing it to ultra violet rays. It retains data even after power is switched off. A transparent window made of quartz crystal at the top of the packaged EPROM allows UV rays to pass through. Devices like microcontrollers use them to store instructions.

Dedicated devices like washing machines have a variant, the OTP PROM (one time programmable EPROM). In this type, the transparent window is not present and the EPROM cannot be erased. This reduces cost.

How an EPROM works:

EPROMs use floating gate technology. A floating gate has a special capacitor that takes an electrical charge (1 or 0). When programming a bit, 1 is changed to 0. This is the on/off state. When the EPROM has to be erased, UV rays are used to change the 0 to 1. Ultra violet rays of frequency UV 253.7 nanometers (2537 angstroms) should be used to erase the data. Instructions are coded using another programming device and algorithms like Standard, Snap, etc.

EPROM selection:

The following specifications must be checked before selecting an EPROM

Logic class an EPROM belongs to like a CMOS or non-CMOS.
The number of address lines available in an EPROM used for data transfer.
Density (Kbits) (e.g. 256)
Number of words (k) (e.g. 128)
Bits per word (bits) (e.g. 8)
Access time, which is, specified in nanoseconds is the time required to locate a particular bit.
Operating current, this is usually in milliamps.
Power dissipation must be as low as possible and is given in milliwatts.
Supply voltage (V) (e.g. 5V, -4.5 V, 3.6 V)
Operating temperature

Application:

Used in embedded program code storage in phones, pagers, modems, machine tools, special machinery, process equipment, etc. Other areas are 1K-bit EPROM for battery pack identification, 8-bit microcontroller, digital signal processors, transcoder DSP, ultra-low-power mixed signal microcontroller, and scanport interface device.