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 file.

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:
     drivername /2
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. Forexample:
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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