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 EPROMs by exposing the chip to ultraviolet light through its quartz window for 15 to 20 minutes, as shown in the Fig. 3.72.
It is not possible to erase selective information, when erased the entire information is lost. The chip can be reprogrammed. This memory is ideally suitable for product development, experimental projects, and college laboratories, since this chip can be reused many times, over.
Erasable Programmable Read Only Memory Programming :
When erased each cell in the EPROMs contains 1. Data is introduced by selectively programming Os into the desired bit locations. Although only Os will be programmed, both 1s and Os can be presented in the data.
During programming address and data are applied to address and data pins of the EPROMs. When the address and data are stable, program pulse is applied to the program input of the EPROM. The program pulse duration is around 50 ms and its amplitude depends on EPROM IC. It is typically 11.5 V to 25 V. In EPROM, it is possible to program any location at any time – either individually, sequentially, or at random.