Over-voltage supplied to AT89S51

!!! over voltage supplied !!!

Hi! This is my first time here. I've searched around for this topic but cannot find. I want to know whether my microcontroller chip is still usable. During attempt to build my own programmer (using AEC_ISP.EXE as downloader and schematic follows the one suggested in the manual) I put 12v DC (coming from PC power supply unit) to one of the pins between 1 and 20, believing it was 5v DC from 7805. I panicked and don't remember which pin it was attached to as I removed it quickly once realising it. It was connected for quite a while possibly more than 5 minutes.

After that I redo the programmer circuit and tried to program it but the AEC_ISP.EXE software failed to program the chip with this error message: "Flash byte error in address 0000". I've rechecked and confirmed (with my little electronics knowledge) that the hardware connection is correct. Now I wonder if the chip itself is a goner. I read the datasheet for AT89S51 and found that absolute maximum rating for voltage to any pin with respect to ground is between -1.0v to +7.0v. But I still wanted to confirm with anyone who knows.

btw the AEC_ISP software was run from DOS real mode, not Windows DOS box. Therefore I think it can control the paralle port directly. If this topic has been discussed elsewhere please redirect me there thank you.

Whether your chip was heated or not???
If yes..your chip is not usable .....

99% the chip is useless.

try out with a new chip

I didn't detect any heat when I ran my finger on it. Anyway I will consider the chip fried. Thanks for the fast reply.

It may be normal by heat. If you cannot Detect / reprogram it or get full functionality, just replace it. Providing about 12 volts for 89 series for even 5 seconds i personally have fired it a couple of times by mistake. Cheers

I built AEC_ISP programmer. After a few tries I finally managed to program the chip. Tough son-of-a-bitch, I say. LOL.

If you use a sophisticated programmer like a Labtool (or a programmer that checks every pin for connection) you will find that the pin you connected 12V to is blown.

The chip will work fine, except for the pin you burned. (provided the burned pin is not one that is needed for programming)

So remember this:
when you write code to turn on an led or something else using that pin, and it does not work, remember what you have done. ( just use another pin)

Cheers