rRemote is a addin for Casio fx9860G calculators written in C. It allows you to send data over the 3-Pin serial port.
You can download the whole project for the official Casio SDK (get it for free from Casio). You can change the serial port parameters in the source code.
The project fxSDK has helped me a lot. You can find documentation about the unofficial syscalls for the serial port there!