Summagraphics MGIII driver for GRASS 4.0 v.digit/GRASS 4.1 v.digit2

This driver is meant for the Summagraphics Microgrid III series
digitizers using a 16 button cursor and 1000 lpi resolution.
It uses Summagraphics Microgrid Universal Input/Output (UIOF) format.
The right (yellow) led on the cursor is used to give a visual response
if the driver detects a button press. If a button is pressed, the driver
waits until it is released.

This code uses BSD port setup, if you don't have /usr/include/sgtty.h,
it will not compile.

The following dip switch settings of the MG III are assumed:

		     DIP #1      |       DIP #2      |       DIP #3
	switch:	1 2 3 4 5 6 7 8  |  1 2 3 4 5 6 7 8  |  1 2 3 4 5 6 7 8
		                 |                   |
	set:	0 1 1 1 1 0 0 U  |  U U U U U U U U  |  U U 0 U U U U U

	key:	0 : off
		1 : on
		U : undefined

	See the manual for documentation on switch combinations.
	The computer serial port characteristics (DIP #1, sw1-7) can
	be changed in D_open_serial() (dig_dev.c). The port operates
	at 9600 baud, 7 data bits, even parity, 1 stop bit.
	Echo mode (DIP #3, sw3) should be disabled.

To change the resolution, change #define SCALE and #define SETRES
in dig_dev.c.
Don't forget to change the third argument of write() in D_digit_init()
and D_digit_setup() (dig_dev.c), if a different initialization is required.

We use this driver with a Summagraphics Microgrid III series 42" * 60"
digitizer. I've heard it works on a Microgrid II series with some
minor changes in dig_dev.c.

Send comments, bugs (and fixes) to: venn@geo.vu.nl

	Raymond Venneker
	Inst. of Earth Sciences	- Vrije Universiteit
	Amsterdam - The Netherlands