Where I work now, I was just working on some old units with a EPROMs that were returned for repair.

Mostly, I've only seen regular EPROMs with the window. I think one company I was working for switched to OTP EPROMs on one product that had been in production and 'stable' for a few years. So, the manufacturers decided to make the EPROMs without the window available at a lower price. In the old days they did have ROMs & PROMs but when EPROMs were introduced they became super-popular and it was a LOT easier to develop, debug, and improve firmware and/or upgrade.Īfter the design & firmware was stable it could be changed to a PROM (or ROM) (less expensive) but they weren't plug-in compatible so the board would have to be re-designed. I'm not familiar with whether the case actually contacts the chip itself, but if the eprom is otherwise unusable there isn't much to lose by trying. A lot of processors use 00 hexidecimal as a no op instruction that does nothing but continue on to the next instruction, so if you have enough unprogrammed memory on the chip, you can overwrite the unwanted code with 0x00 and the processor will run through all the No-op instructions until it reaches the code you want to run.Īnother option might be to mill a hole in the casing in the position used for the quartz window. All bits are set to a logic 1 in the erase state, and are programmed to a logic 0 state. The chip may still be usable, depending on your intended use, and what the current contents of the memory are. The OTP variant (One Time Programmable) is not erasable because it has the solid case that does not allow exposure to UV. The quartz window is not there to satisfy your curiosity, the memory is erased by exposure to ultraviolet light, so there has to be a way to expose the chip to the light.

27c256 eprom programmer arduino