Summagraphics Bit Pad One GPIB protocol documentation?

[Josh Dersch]

I'm working on supporting GPIB tablet support for PERQemu (right now it 
only supports the 3-button Kriz tablet).  Anyone have documentation for 
the protocol used by the GPIB variant of the Summagraphics Bit Pad One?

I've found documentation covering the Bit Pad Two 
(http://www.calcomp.com/files/Bit%20Pad%202%20Tech%20Ref.pdf) , which 
appears to be RS-232 only.  I'm sure the protocols are similar, anyone 
know for sure?

Thanks,
Josh