Serial Modem data break problems

Scott Copeland copelands at
Fri May 28 09:49:17 EDT 2004

I'm developing a test fixture for an embedded modem product and am having
some problems breaking out of data mode.  Here's the protocol in a nutshell:

Open COM port  -> works
Send "AT"  -> works
Look for "OK" -> works
Send "AT&T1" -> works (enter internal loopback)
Send "ABCD...." -> works
Look for "ABCD...." -> works
   <1 second delay>"+++"<1 second delay>   -> doesn't work
Look for "OK"

For some reason, the modem is not breaking out and back into command mode.
I verified the whole protocol using Hyperterminal.  I've also created a
button that just sends the BREAK and that works.  I can tell that the modem
is not seeing the BREAK by going back into Hyperterminal and sending the
AT...which gets echo'ed back.  That tells me it's still in loopback mode.
By the way, the BREAK on my modem only requires about 300ms before and
after.  I'm using 1000ms for test purposes.

Any ideas?



Copeland Communications, Inc.

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