hi,



We have already discussed the boot process of Atmel X2 chips many times here.

And once again, AT89C51RD2/ED2 datasheet says at page 102:

Bootloader Functionality

The bootloader can be activated by two means:
Hardware conditions or regular boot process.

The Hardware conditions (EA = 1, PSEN = 0) during
the Reset falling edge force the on-chip bootloader execution.

As PSEN is a an output port in normal operating mode
after reset, user application should take care
to release PSEN after falling edge of reset signal.
The hardware conditions are sampled at reset signal
falling edge, thus they can be released at any time
when reset input is low.

To ensure correct microcontroller startup,
the PSEN pin should not be tied to ground during power-on.

So this ordinary idea about button/jumper etc is not correct due datasheet notes. I cannot remember who here said about that Atmel even notices such way may damage derivative.

Indeed, most users including me still do this way.
But the question is: should we provide the wrong way for begginners from the start?

Regards,
Oleg