Mega2560 Serial Wiring Diagram?

Hi. I've just got a Mega2560 to try to interface to some products at work via Serial. Remembering that the LEDs needed a resistor in line on a Digital Out, I didn't want to do anything stupid so I went through the online docs and found this:

On the diagram, it shows a straight connection between the ATMega and the Serial Device. So, I followed the instructions there and connected all the wires directly to the Arduino, using Serial Port 2. No joy.

I then searched deeper and found this link:

In it there is a disclaimer later on that says:

(Don't connect these pins directly to an RS232 serial port; they operate at +/- 12V and can damage your Arduino board.)

So, I'm confused. Which is it? Do I need to have some sort of resistor to buffer the Rx/Tx going into the Arduino? If so, what type? How do I work this out by myself? Obviously I don't want to blow anything on the chip's side, but I've tried Google and come up with nothing as well.

Does anyone have a wiring diagram that shows how to connect this properly? And is there a way to get this info into the main documentation so that this is more straight-forward for other idiots like me? ;)

Thanks in advance.

You can't connect an RS232 signal direct to an arduino it has to go through a converter. This is because the voltage is different and the logic level is inverted. Normally you will use a driver chip to do this, there are lots and lots of chips that do this. The MAX202 is one I use a lot, just google it.

Perfect. Thanks. Looks like I can get it locally.

Any particular reason why you use the Max202 instead of other chips? (I see there's a Max232 as well ...)

Any particular reason why you use the Max202 instead of other chips

Yes I got a box full given to me by maxim many years ago and I am still working through them. ;)

Lol. Nice. Enjoy, then. I'll see what I can find over this side as the one supplier wants about double the U.S. price for chips. The price we pay for our addictions ... ;)