Kai Klaas wrote:
-------------------------------
Are you sure you 'hit' the XTAL-input?

Thanks for making me double check everything! I hit the XTAL output instead of the input... There was an error in the schematic symbol for the AT89C2051 - the XTAL pins were swapped. Which of course would cause no problems in normal circuits...

After fixing that problem I was able to read the second signature byte also. But I still couldn't programme the chip. I checked all logic levels during programming with a logic probe, and everything was as described in the datasheet.

After that I tried inserting pauses various places in the code to be able to monitor what was happening, and everything looked fine. Then I tried with the chip installed, and now it worked! After some tests I determined that I have to insert a 2.5ms break after powering up the chip before programming the first byte. Why should that be nescessary? I don't need any pauses before reading the signature, blank checking or erasing the chip, and the rest of the timing is done according to the datasheet...

But I just made the pause 5ms to be safe, and everything seems to work fine now. Now I only have 20 more chips or so to figure out ;-)

Best regards,

Mikkel C. Simonsen

Good luck,

Thanks.