EEPROM and OTP different why?

[Mark Scotford]

This is a continuation of another thread, where I thought that my IcePic2 was acting differently than my EEPROM 17C756A. It transpires that if I try and run my code on any of the four EEPROM 17C756A's I have, I get the same couple of inputs not working properly. If I blow the same program into an OTP version of the same chip, then everything starts acting the way it should again, my question is, what is the difference between an EEPROM and a OTP version of the same chip (all inputs have external pull-ups). Your help would be very much appreciated. TIA

[Mark Scotford]

Sorry that should have read EPROM not EEPROM (I'm tired)

[BobK]

Hi Mark.

EPROM means "erasable programable read only memory". OTP means "one time programmable". Once you program an OTP chip that's it! You can't program it again. These types of chips are generally used for production devices where the chip will never be re-programmed again.

An EPROM based chip can be re-programmed only after exposing the window on the chip to ultraviolet light in a chip eraser for the required amount of time then checking to make sure it is blank. This takes time, like more than 20 minutes sometimes. Actual time is usually specified by the chip manufacturer.

The newer Flash memory chips are what you should be using to create projects. In seconds you can blank the chip and download a new program into the chip and then test and retest your project. It's really the way to go today!

BobK