I have looked about and can't find a clear answer to the following question. If I program a standard Uno through its USB connector, I involve the hardware serial port on the chip, so it isn't easy to use those two pins for other things.
But, if am programming something like the ProMini using and FTDI adapter, if the hardware serial port on the Atmega 328 still involved, or does it become avialable for other uses?
Thanks in advance for any help.
A Pro Mini with an FTDI adapter is basically an Uno. If you look at the schematics for both, you will see the hookup is the same, and the consequences of using the serial port is the same.
program a Pro Mini and detach the FTDI adapter and use the serial port pins for other things,
it is essentially the same as if you:
program an UNO and then choose to not use the onboard USB-to-serial adapter after programming, and use the serial port pins for other things.
The only differences you may notice are subtle. For example, since TX from the USB-to-serial adapter chip is normally held high when it is not actively transmitting, the ATmega328P RX pin will be pulled up. If you're doing something with that particular pin which requires that to be pulled down or float, you will need to adapt or improvise. If you are using an Arduino with a detachable USB-to-serial adapter, and you detach it, that is not going to be a concern. If you fail to detach it, it will be more of a concern, because FTDI adapters may not have the series resistors (often 1K) you see between the USB-to-serial chip and the main processor RX and TX pins on the Uno or other all-in-one Arduinos.
Check out the schematics to see all the impacts. If you look at the schematic for the Proto Snap Pro Mini you can see the FTDI adapter and Pro Mini all on one page. Schematic links from these pages: SparkFun ProtoSnap - Pro Mini - DEV-10889 - SparkFun Electronics https://www.arduino.cc/en/Main/ArduinoBoardUno