Comtrol RocketPort Windows 98 - Manual (Page 37)

Troubleshooting 37
Windows 95/98
Bypassing the Normal Windows 32 API s
An application program cannot talk to the port driver directly, and
must go through the normal API calls. In the Windows 95/98
environment it is possible to write a VCOMM client to bypass the
Win32 API layer, but this is not recommended and is not portable to
the Windows NT environment.
Real Time Issues
The driver runs in a polled interrupt fashion; the system is
interrupted every poll period. The poll period default is 10
milliseconds (100 Hz).
What this means is that all Event processing is restricted to the poll
period interval. This will only be a problem for some applications that
require very precise synchronization with other hardware. In some
cases, this may be worked around by polling the queue counts through
GetCommError().
Opening Ports Higher Than COM10
In order to open up COM ports higher than COM10 a special named
format is used with CreateFile(): \\.\COM10 (when using the C language
you need to double up the backslashes: \\.\COM10. This works only for
32-bit programs running under Windows NT or Windows 95/98. In
Windows 3.1 there is no provision for opening COM ports above
COM10. Comtrol had developed a custom library to work around this
problem under Windows 3.1. 16-bit applications running under
Windows NT or Windows 95/98 also have this restriction.
COMMTIMEOUTS :
GetCommTimeouts() and SetCommTimeouts() Structure
These features are implemented in a standard part of the operating
system and not in the port-driver, although it does rely on callback
facilities built into the driver. These timeouts should be used to avoid
getting stuck forever in a read or write operation when using the
standard (non-overlapped) mode of operation.