Greg London wrote: > ...I don't understand how the DTR/RST from the USB FTDI works when > its connected to reset via a cap.
I'll start with the disclaimer that I haven't done any Arduino hacking. The generic answer to your question is that the designer is using AC coupling. Perhaps that's obvious. When DTR goes low, it'll briefly pull down the micro's reset pin. Here's a bit of Arduino specific info that might shed some light on why this arrangement exists: http://www.sparkfun.com/products/8772 The major difference with this board is that it brings out the DTR pin as opposed to the RTS pin of the FTDI cable. The DTR pin allows an Arduino target to auto-reset when a new Sketch is downloaded. This is a really nice feature to have and allows a sketch to be downloaded without having to hit the reset button. This board will auto reset any Arduino board that has the reset pin brought out to a 6-pin connector. This also explains who is initiating and who is receiving the reset signal. It seems like there is a typo in one of the documents being referenced with regards to RTS vs. RST. It seems likely that the schematic you referenced had the typo, and should have labeled that pin RTS (Request to Send), as it is sometimes used for the same function[1] as the Data Terminal Ready (DTR) pin. This page (about hacking a cheap FTDI to be Arduino compatible): http://rajeshkovvuri.wordpress.com/2011/11/02/ftdi-type-usb-uart-adapter-for-3-2/ mentions that the FTDI chip also has a RST pin, but says: The trace to RST needs to be cut(this RST is related to usb) and re-wired to GND 1. http://en.wikipedia.org/wiki/Data_Terminal_Ready#As_used_on_serial_printers -Tom _______________________________________________ Hardwarehacking mailing list [email protected] http://lists.blu.org/mailman/listinfo/hardwarehacking
