...I've analyzed the (simple) schematic of the xbee explorer regulated ( http://www.sparkfun.com/commerce/...ts_id=9132 ) and from what I'm seeing this board has nothing but a 3.3V voltage regulator. As I see it now the problem lies in 'stepping up' the voltage level of the Dout pin of the Xbee to 5V so my 8051 core microcontroller UART can recognize the levels. This isn't an issue, I think, since I am only sending data from the microcontroller to the PC, hence I'm really only utilizing the 8051's P3.1 (TxD) and the Xbees Dout, but for the sake of an elegant design....I'd like to 'solve' that. I don't think it will be much of a problem. On top of my head I think if I connect a diode between the 3.3V output (cathode-Dout) and the 5V input (anode-P3.1/TxD) and I use a pull-up resistor on the 5V side, I should solve the problem. I could use a shottkey diode since it drops less voltage then common silicon diodes? It'll serve to protect excess voltage from damaging the TxD port of the 8051.

So that is probably solved. Although oh well. It's also an inelegant solution due to 'slow' switching times of the diode. But anyway it should get the job done.

The last thing that I cannot understand is why the diode, again upon first inspection of the xbee explorer regulated schema (here's the link again: http://www.sparkfun.com/commerce/...ts_id=9132 ) is...reversed biased? Isn't the 8051 UART logic level between 0 and 5V? I do understand that the diode will drop some voltage on it to guarantee a safer voltage to interface the Xbee (as in my case), but....still, why the diode's polarity is like that? It is probably a very stupid question and/or I'm missing something out. But I want to understand.

Thanks guys,

Kai