Kai Klaas wrote:
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> 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?

As long as I don't know more about your circuit, I can only guess: There can be some time 'constants' in your ciruit, needing this few milliseconds.

Here is the schematic - complete with XTAL pin error: Schematic

The 7407 doesn't really serve any purpose BTW - except for the "E" gate. I put it there to be able to get non-totempole outputs (PB is a 574 latch), but that's not nescessary it turns out.

I guess there could be "constants" somewhere, but I can't figure out why they would only apply when programming the chip...

Another guess: When using built-in oscillator in combination with quartz, mcu is allowed to need some milliseconds for stabilizing. May be that mcu needs this time for some other stuff, also? Sometimes in datasheet such a minimum time needed for being ready for programming after power-up is specified. I cannot remember where I saw this, but I did.

I have seen it in Infineon datasheets, but the oscillator is given as the only reason for the delay.

It's a only a feeling, but I would insert even a longer break for stabilizing: Something arround 10...20msec.

I probably should. I will test the circuit with different chips to find the minimum value, and then set the time three or four times higher.

Best regards,

Mikkel C. Simonsen