I set up my breadboard (i.e. atmega168, ftdi232r chip) based on the diecimila schematics and everything’s working as it should. Previously while troubleshooting though I observed some odd behavior on the DTR / auto-reset line. With a 100nF cap connected to the reset line and a 15k pullup the line goes to 0v immediately and then slowly charges back up to 5v - so far so good. Right after that, however, the line immediately goes up to 10v and then slowly goes back down to 5v. The same behavior was observed here (note that I am using USB only, not serial though) : http://www.arduino.cc/playground/Learning/AutoResetRetrofit
My questions are:
a) how can there be 10v if the supply is only 5v from the USB bus ?
b) is this pulse (which lasts more than 100 uSecs) harmful to either the FT232R or the atmega168 ?