EPROM

Working with ROMs and PROMs can be a wasteful business. Even though they are inexpensive per chip, the cost can add up over time. Erasable programmable read-only memory(EPROM) addresses this issue. EPROM chips can be rewritten many times. Erasing an EPROMs are configured using an EPROM programmer that providevoltage at specified levels depending on the type of EPROM used.

This charge causes the floating gate transistor to act like an electron gun. The excited eletron and pushed through and trapped on the other side of the thin oxide layer, giving it a negative charge. These negatively charged electrons act as a barrier between the control gate and the floating gate. A device called a cell sensor monitors the level of the charge passing through the floating gate. If the flow through the gate is greater than 50 percent of the charge, it has a value of 1. When the charge passing through drops below the 50 percent threshold the value changes to 0. A blank EPROM has all of the gates fully open, given each cell a value of 1.