It really depends on the controller and how it functions, you need to break out the DMM and figure that kind of thing out, or look it up.
The CG/2/3 version boards all have Common Ground buttons, so all you do is drive the IO line of the PIC connected to the button line of the controller Lo to make that function happen.
For example: If you take the typical 12F683 and wire it up so the GPIO1 pin is connected to the A button line, then code it to make that IO line go Hi (pause 1 second) Lo (pause 1 second) Hi, etc, etc forever..
while(1)
{
GP1_bit = 1;
delay_ms(1000);
GP1_bit = 0;
delay_ms(1000);
}
.. then it will sit there the same as you pressing the A button manually over and over and over again.
The Triggers in the CG/2/3 however are Analog, and need to be driven Hi (1.5v) to fire, but the IO lines of the PIC there must be configured as inputs (hi Z, TRI-Stated) when not being used by the PIC so the Triggers can function normally.
If you can make LEDs blink by turning the Cathodes (grounds) to them on/off, then you can do any of the 16 buttons in the CG version controllers, since grounding LED Cathode = LED on, is the same thing as grounding button line in controller = button pressed.