Kai,

I could then put it this way:

8051 has diodes on input, but that's a by-product inherent to the technology used an as such not to be used as protection device for inputs.

If inputs need to be protected, then make sure that these are activated below Vcc+0.5V or above GND-0.5V. (ie protection must trigger _before_ pn-junctions trigger.)

thanks for the effort

Patrick