AccessPoint's,  I/O Device Driver Toolkit, has a library of I/O source for use by integrators: 

Drivers from various product releases, not all of them work with the present release - but source is available for modifIcation. 
THERE IS NO WARRANTY WITH THESE DRIVERS they are SOLD AS IS.

Allen Bradley KT Card
Allen Bradley Serial I/O
Simulation I/O
Digitronics SixNet 60
General Electric Series 6
Hewlett Packard RTU
Modem Kernel
Modicon
ModBus Plus
Opto 22
PeerPath
Siemens 3964
Siemens H1
Square D
Texas Instruments
Vericom