If you use the Topcon 'Topsurv' or 'Magnet' range of survey or Machine Control equipment then the following links will prove of interest.
Trimble CAL to Topcon GC3 data exchange
A free Windows application which converts Trimble calibration (CAL) files containing local site or map projection data into a Topcon localization (GC3) file for use in Machine Control. Visit our product page here
Here's a copy of our feature coding document (Acrobat format)