Can I use the hardware serial pins that are built in to the Arduino as communication between my ID-12 Innovations RFID reader? I keep seeing people use the AFSoftSerial library to communicate with it, and I wanted to know why.
Yes, in principle you can use the hardware serial pins for that. But, the Arduino already uses those pins to connect to the FTDI USB chip, for bootloading code. So, there may be a conflict, which is why people use software serial instead.
Well the Arduino hardware send and receive pins are 'hardwired" on the board to the USB serial converter chip. That's not necessarily a problem for the Arduino send data pin as sending to two input devices is electrically OK, however it's a problem for the Arduino input pin as an external signal will be trying to 'fight' with the output signal from the USB chip. There are two series resistors between the USB signals and the Arduino serial pins so I don't think there would be any permanent damage, and I've never tried to do that (share the hardware serial port with two devices) but it seems from other posting of problems and advice that it is not a good solution.
Anyway going to softserial eliminates the problem by then using physically different pins that have no other electrical connections to anything else.
Lefty
Crap.
I ordered a custom shield PCB not knowing that. Damn. 30 bucks down the drain.
I don't intend to have the board connected to my computer at the same time as the ID-12 is. Does the FT232 still transmit data to the ATmega 168 after a sketch has been uploaded and the board has been disconnected from the computer?
"Does the FT232 still transmit data to the ATmega 168 after a sketch has been uploaded and the board has been disconnected from the computer? "
No it doesn't transmit any data, but it's chip is still powered up by the same 5vdc that powers the rest of the board so it's TTL output pin going to the Arduino's serial input pin is still electrically active, most likely sending a steady HIGH signal. If you could somehow not hook your external serial signal to the Arduino until after you disconnect the USB cable and then connect it, I think that might work, but again you are kind of on your own as it's untested by me and others would have to be sought out if it has worked for them.
Lefty