This is the command I use to switch from command mode to data mode,  that
causes the modem goes off line.

m_MSComm.Output = "ATO0" & ControlChars.Cr

If anyone has experienced this situation, please give a hint.

Thanks in advance,
Quynh

This command tells the modem to ORIGINATE a connection.  It cannot be issued
when a modem answers.  If you wanted to do that, you would issue an ATA
command.

However... If the modem is configured to auto-answer, then if you send ANY
command while the modem is answering, the modem will disconnect.  This is
the standard mode of operation.   Auto-answer means that no command is
needed to complete the connection.

If you do not configure the modem to auto-answer, then you may issue the ATA
command while the modem is ringing.  The modem will then go offhook and
attempt to connect in answer mode.

--
Richard Grier  (Microsoft Visual Basic MVP)

See www.hardandsoftware.net for contact information.

Author of Visual Basic Programmer's Guide to Serial Communications, 3rd
Edition ISBN 1-890422-27-4 (391 pages) published February 2002.

Richard,

Thank you very much for helping me out.  I understand it now.
I should not issue any other command after issuing an AT command to place
the modem in
"Auto-answer mode"  (m_MSComm.Output = "ATS0=1" & Controlchars.Cr).
Otherwise the modem  the modem will disconnect.

I have been learning a lot from you and your book.

Thanks
Quynh

Correct me if I'm wrong, but you should be able to send "+++" to the modem
to get it into command mode from data mode.  I'm not sure if that will
cause a disconnect.

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