GHS Bulletin - Digitizer (version 3/3/95)
Interfacing a Digitizer with Section Editor
The SE program interfaces with most digitizers through ADI drivers. The
driver is a small memory-resident program which stands between the digitizer
hardware and an application program such as SE. The ADI standard was
established by AutoDesk (manufacturer of AutoCAD) and is therefore very
commonly used. Most likely your digitizer came with an ADI driver file.
There are two forms of drivers: "Real Mode" and "Protected Mode". SE uses
the Real Mode form. For example, most mouse drivers are in Real Mode form.
Typically you install a Real Mode driver by executing an .EXE file. Some
drivers are supplied as a .SYS file which must be installed by including a
DEVICE statement in the CONFIG.SYS file which references the driver's .SYS
When you install the driver you typically give a parameter indicating which
serial port the digitizer is attached to. You may also have to specify the
baud rate, etc., but usually the driver will sense that automatically. The
exact details of the parameters you need to use when installing the driver
should be provided by the documentation which came with the digitizer.
If your digitizer is connected to serial port #1, you may find that the driver
can be installed successfully without using any parameters. If it is
connected to another port, the port number is commonly conveyed using only a
slash followed by the port number. For example port #2 would be:
Real Mode ADI drivers communicate with the application through a "software
interrupt vector" which is identified by a particular "interrupt number".
Since AutoCAD uses interrupt 121 (79 hexidecimal) this is the interrupt number
which the driver will most likely assume by default. Likewise, SE assumes
interrupt 121. SE and the ADI driver must both be using the same interrupt
number in order to communicate.
SE supports two kinds of digitizers directly, without the need for a driver.
These are the Summagraphics MM 1201 series and the Calcomp 9100 series.
When using SE with either of these digitizers and without a driver, you must
set the communication parameters of the serial port to agree with the settings
used by the digitizer. This is done by means of the MODE command in DOS.
MODE COM1: BAUD=9600 PARITY=ODD DATA=8 STOP=1
sets the communication parameters of serial port #1 to 9600 baud, etc. Once
set, these parameters will remain in effect until changed by another program
or until the computer is restarted. Once you have established the parameters
you will be using, you can make a little batch file with the proper MODE
command in it. Thereafter, you can set the communication parameters merely
bytyping the name of the batch file.
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