Below is an edited extract from an [[http://groups.google.com.au/group/mod.mac/browse_thread/thread/d6cec207212feaa1/82203172bc987e03?lnk=st&q=summagraphics+mactablet+driver+&rnum=8&hl=en#82203172bc987e03| email I found]] on Google's Usenet Archive.  I think there is enough information in there to allow us to use some older serial port graphics tablets as X-Y controllers under MIOS. 

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DrBunsen.


''Date: Sat, 26 Jul 86 09:12:59 pdt''\\
''From: oster%ucbla...@BERKELEY.EDU (David Phillip Oster)''\\
''Subject: Re: Digitizing point coordinates (MacTablet)''\\

This letter discusses using Mac compatible digitizing tablets to get high
resolution data ... since you are not afraid to program, you might try the following:

I assume the MacTablet connects to the Mac using a serial port...

Listen to the tablet using terminal software (Versaterm, naacterm ...)(try 9600 baud as an initial guess at the baud rate.)

The tablet probably sends a 5 byte data packet of the following form:

^  b7^  b6^  b5^  b4^  b3^  b2^  b1^  b0|bits of a byte  |
|  P|  1|  0|  0|  0|  S|  0|  0|P is parity.  S is on if switch is down  |
|  P|  0|  x5|  x4|  x3|  x2|  x1|  x0|low 6 bits of x data  |
|  P|  0|  x11|  x10|  x9|  x8|  x7|  b6|high 6 bits of x data  |
|  P|  0|  y5|  y4|  y3|  y2|  y1|  y0|low 6 bits y data  |
|  P|  0|  y11|  y10|  y9|  y8|  y7|  y6|high 6 bits y data  |


b6 is 1 only at the start of a 5 byte data packet.

This data is drawn from a Summagraphics data sheet for their Bit Pad 1
digitizer.

Unlike the Mac, point (0,0) is probably at the LOWER-left corner.

If you get data that is consistent with this, then you need only write a
basic program to read data at the serial port.  Tablets generate so much data
that you're program had better check the fullness of the serial buffer and
throw away 5 byte data packets periodically to keep the buffer from
overflowing.  Alternatively, you could write in a language, like C or
compiled Pascal, that was fast enough to keep up with the data rate.

Low-resolution Kurta tablets and other-than-MacTablet Summagraphic tablets use this data format when they
are not transmitting data as strings of ASCII, base-10 integers.

Kurta's PenMouse, a cordless digitizer considerably cheaper than
MacTablet, sends 2400 baud, their other models generally run at 4800 baud.
Kurta also makes a MacXL compatible version.

Disclaimer: My opinions are solely my own, but, in evaluating them, you
should know that I am currently re-writing Kurta's software.

--- David Phillip Oster         -- "The goal of Computer Science is to\\
Arpa: o...@lapis.berkeley.edu  -- build something that will last at\\
Uucp: ucbvax!ucblapis!oster     -- least until we've finished building it."\\