I'd like to use a RFID reader with my Arduino Duemilanove. The RFID module communicates using TTL RS232, which means I need to connect it to the UART RX and TX pins of the Arduino.
What happens to the FTDI USB port connected already to the RX and TX pins? Would this cause trouble when trying to upload firmware to the Arduino?
Whether the RFID reader interferes with uploading sketches depends on how the RFID reader is powered. If the RFID reader is a low current device (mine is), you could power it from a digital pin. Use digitalWrite to set the pin HIGH to power the reader. Then, when a sketch needs to be uploaded, a reset occurs, setting the pin back to LOW, powering off the reader, allowing uploads to occur without problems.
Or, you could use NewSoftSerial to communicate with the reader, and not connect it to the RX and TX pins at all. Simply use another pair.