YI, I just tried another little experiment (modified)I took a 110 ohm resistor and connected the arduino 5v pin to the reset pin, jumper style. They are close together.Guess what? No more com port resets SmileyRemove the jumper resistor and com port resets resume.The 110 ohm resistor is just enough to keep the reset pin high (2.38v) when the ftdi chip tries to pull it low, and limits the current through the ftdi pins to 24ma*. It also limits the current through the reset switch to 45ma.for reference:http://www.arduino.cc/en/uploads/Main/Arduino-Diecimila-schematic.pdfhttp://www.ftdichip.com/Documents/DataSheets/DS_FT232R.pdfI don't know that I would trust it with an isp conected either. But it seems to be a simple "jumper style" solution, just have to make the jumper out of a 110 ohm resistor with some nice thick leads that fit the in the headers nicely.*24ma is the limit on the ftdi rts/dtr pins, if I'm reading the datasheet right. Don't go below 110 ohms. I think you can go up to 124 ohms before it will start resetting anyway.
also, a 47 ohm resistor between 3.3v and reset seems to prevent serial resets. It's a more common value and leaves the 5v pin open. But if you hit the reset switch it it will draw 70 ma from the ftdi 3.3V port while the switch is closed, and the datasheet lists 50ma max. I tapped my reset button a few times with this configuration and the magic smoke stayed put, and upload still worked when I pulled out the resistor, but I can't really recommend the 47 ohm if you are planning on using the reset switch.
Re: disable auto-reset by serial connectionReply #2 - 04.03.2008 at 16:04:03 There is a hardware solution: to remove the 100nF cap (I think it's labeled as R3). Since the cap is smd type, depending on your soldering equipment and skil, this change will make some ruin on board.I saw some discussion about software solution, but I don't know where, and I don't remember if it was sucessful.
on the newest boards (cant remember name the ones without the power jumper) there is a track near the usb port and it has 2 solder pads if you cut the track between these pads the board wont reset and you can solder it back together later