I've used the RFM12B modules with PICs. I think the interface is identical. I don't have C code, but the manufacturer, HopeRF, has code in C in their datasheet. It's pretty simple, mine worked first try.
I'm still fighting against 2 x RFM22B S2 modules to get them working with a PIC. ( i use a 18F2620 )
I simply would like to get a working demo because i can't get communication working on these modules.
I've spend long time on the datasheet and on the Hoperf demo code without success.
I will really appreciate if someone would share a working demo code, ie sending a demo sentence 'Hello World' to the distant module.
However this code was already my base of work, actually I've tried to get inspired from that code ( it was written for Atmel µC ) but i think i was not able to port it for PIC properly , since it does not get transmission working from here.
It could be helpful if has a working for written in C18 or XC8 for PIC µC.