How to use RS-232 sheild as software serial port?
GND => GND 5V => 5V Digital Pin 2 => 232RXD Digital Pin 3 => 232TXD


A better choice of board would be the Leonardo, since you could connect such a shield and use the USB port right out of the box. However, since you have the Uno, there is a solution.

From Arduino:


  The SoftwareSerial library has been developed to allow serial communication on other digital pins of the Arduino, using software to replicate the functionality (hence the name "SoftwareSerial"). It is possible to have multiple software serial ports with speeds up to 115200 bps. A parameter enables inverted signaling for devices which require that protocol.


It then goes on to reccomend the library AltSoftSerial.

Here is some example code from the link above:

#include &lt;AltSoftSerial.h&gt;

AltSoftSerial altSerial;

void setup() {
  Serial.begin(9600);
  Serial.println("AltSoftSerial Test Begin");
  altSerial.begin(9600);
  altSerial.println("Hello World");
}

void loop() {
  char c;

  if (Serial.available()) {
    c = Serial.read();
    altSerial.print(c);
  }
  if (altSerial.available()) {
    c = altSerial.read();
    Serial.print(c);
  }
}


It acts like a standard serial port, only you declare the connection as a variable first. This code is written for a board with an additional serial port, like you have.

All is good, except for one problem:

The problem is the shield is wired to connect to pins 0 and 1: the ones used by the USB adapter. The AltSoftSerial library uses pins 8 for TX and 9 for RX. (Note: You cannot use PWM on pin 10 on the Uno... it should still work as a digital pin.) In that case you would not attach the shield by plugging it into the Arduino, and you would wire it like this:


  GND => GND | 5V => 5V | Digital Pin 8 => 232RXD pin 0 on the shield headers | Digital Pin 9 => 232TXD 1 on the shield headers


So then, you would be manually wiring the shield to the Arduino with jumpers. As long as it doesn't connect to any other Arduino pins I'm not aware of (it shouldn't besides maybe 13 for a LED or something like that), it should function like it would stacked and using pins 0 and 1.

Note: (Obviously) You cannot connect anything to the headers on the shield (You cannot connect to pin 5 and get a signal).