KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q103637: Use EV_RINGTE for Modem Ring Detection

Article: Q103637
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 06-NOV-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) 3.1 
-------------------------------------------------------------------------------

SUMMARY
=======

Many communications applications need ring detection. The documentation for
SetCommState() indicates that EV_RING should be the event to set for this
purpose. However, the EV_RING bit does not work as expected; the EV_RINGTE (ring
indicator trailing edge) event should be used for ring detection.

The trailing edge of the ring indicator (RI) generates a modem status register
(MSR) interrupt, which in turn sets the EV_RINGTE bit. EV_RING is set to the
current status of RI. Because the interrupt does not occur until RI changes from
high to low, EV_RING almost always is low (except when it happens to be high
during another MSR interrupt).

The EV_RINGTE event is not referenced in the SetCommEventMask() documentation;
however, it is defined in WINDOWS.H, and will be supported in future versions of
16-bit Windows.

NOTE: The information in this article applies to the 16-bit comm driver in
Windows 95 also.

EV_RING
-------

EV_RING is set when the ring indicator is detected high during Modem Status
Register (MSR) interrupt processing. This is an absolute state, but since it is
read only during MSR interrupt processing, it will almost always be zero. The
only time it will not be zero is when the ring indicator is high and the MSR
interrupt is triggered for some other reason, such as a change in the state of a
line (CD, CTS, or DSR). Because of this, EV_RING has no real value for detecting
a ring.

EV_RINGTE
---------

EV_RINGTE is set when a ring is detected on the modem. The trailing edge of a
ring indicator generates an MSR interrupt, which in turn sets the EV_RINGTE
event. Use this event to detect a ring.

Additional query words: 3.10 Win16 no32bit COMM SetCommState event

======================================================================
Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version           : WINDOWS:3.1

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.