Are you holding the 16u2 in reset?
Ground the reset pin on the ICSP header FOR THE 16U2.
Thanks. I'll try that tonight.
I have an Uno R3 that works just fine with the built-in USB interface. I have a need to test some PC software with an FTDI232 interface, instead of the 16U2 USB chip on the Uno R3. Looking at the schematic, the 16U2 TX/RX lines go to the TX/RX lines on the 328P and the Uno header.I plugged the TX/RX lines from an FTDI board (that I know works with Pro Minis), along with a GND connection. The Uno is powered via the USB port, but the data lines are not connected, only power and ground. No matter which way I swap the TX/RX lines, the PC does not see the Uno with the FTDI board.Basically, what I am trying to make is an earlier version of the Uno, but I don't have one on hand. This is for a one time test, to determine why some PC software isn't communicating.Can anyone help?
Buy yourself a Duemilanove. It's an Uno with the FTDI serial interface chip
My assumption would be the pins would be tristated but now I'm not sure.