Remote Access via modem


Thread Starter

Donny Zimmerman

I am working on my first project of connecting to an AB Micrologix 1000 via modem and DF1 protocol. I do not have two phone lines so the only way I can test the auto answer on the modem is through a switchboard at work. I have set the modem to auto answer and the S register to answer at 1 ring. The second line rings but the modem's auto answer light just flashes at every ring and does not answer. I thought maybe the modem was bad so I tried a second (different brand) and it does the exact same thing. I have gone through the AT Commands and I cannot figure out what I am missing. I have a hard time believing that the modem can tell the line is ringing through a switchboard and that it should answer, (the ring sounds like a normal phone). I am going to try to get a friend to call my line at home, but it would be nice to test my systems at work.

Hope someone can help. Thanks

(P.S. my goal is to access the data tables with my Visual Basic program and an ActiveX control which I have gotten to work with a direct connection. The ActiveX has functions for dialing out which I have gotten to work, just can't get the other end to answer.)
If it rings that is good as far as your testing goes at work. I would call the modem manufacturer support line if possible. Everytime I have ran into this they have had to address the problem before and were able to walk me through a fix or the proper settings for the situation.

I ever do this before and it work. maybe your problem in the AT command or the register, there is some miss i guest.

try this setting for your modem :
ATS0=... "..." it must higher than 0
ATS1=... "..." it must higher than 0
AT&D0 it must becouse the command for the auto answer enable (the modem ready auto answer)
as far i know, the modem can not auto answer in 1 ring, but 3 ring =<.

I think your device can not run, if you use digital line (PBX system), try use free line or not PBX system. But if you just want to auto
answer, modem can answer through digital line PBX system) becouse i ever try.
The configuration you are describing should work. Do you have the modem configured to output result codes? You want those off in this case
because otherwise the connected device (Micrologix, etc.) sees the result codes and may either echo them or respond with jibberish. Many
modems will abort a connect attempt if they recieved unexpected comms on ther serial port during the handshake process. The other possibility is that the modem is actually answering and then disconnecting because it does not detect a carrier. One common mistake that causes this if when the cable is plugged into the wrong jack on the modem (the one intended
for a telephone). The modem sees the ring and disables the phone jack as it goes off hook (so that someone picking up the handset won't
interfere with a data connection), thereby disconnecting itself. This is a more common mistake than you might guess!


Jerry Miille

It is not that uncommon for a modem to not be able to "hear" the phone ringing. Modern day modems look not only for a ring voltage but also, the level, frequency and waveform. It is quite possible that the ring signal coming out of your switchboard is not compatible.

Some industrial modems can override this checking and may work for you. One example is our DIN rail mounted dial-up modem "":

You can contact me off list if you have any further questions.

Jerry Miille ([email protected])