Technical data

Linkage with PLC
122 VIPA GmbH CP486 ⋅ 00/14
6.3.2.5 Parameterization of File Accesses via Handles
The COM-driver allows full access to all drives of the CP and supports access to directories. For
every file access a drive and/or directory name can be specified and the same rules are valid, as
known from MS-DOS.
To access files under MS-DOS numbers, the so called handles are used. The amount of available
handles and herewith the maximum number of open files at the same time is specified by the entry
FILES = n in the CONFIG.SYS. We recommend to set the FILES-parameter at a minimum of 20,
better however to 25 or 30.
By means of handles not only files on a mass storage, like hard disk, RAM disk or disk can be
accessed. MS-DOS offers the opportunity to access via handles so called devices as well, like
printer and serial interfaces. For a series of devices standard handles have already been defined.
These devices need not to be opened before they are accessed. By direct read or write functions data
can be read or output. Thus the PC can in easy way directly access printer, screen and keyboard of
the CP486.
Predefined Standard-Handles
Handle Device access mode
00 standard-input (keyboard), read only
01 standard-output (screen), write only
02 standard-error (screen too), write only
03 standard-auxiliary (V24-interface), read and write
04 standard-printer (auxiliary), write only