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Old 56k Modem Connection Dialog Question — Parallax Forums

Old 56k Modem Connection Dialog Question

xanatosxanatos Posts: 1,120
edited 2014-09-09 16:13 in General Discussion
I'm delving into the retro-world of 56k dialup modems.

I'm using Terminal at the moment to get two modems (yes, they're on different phone lines) to talk to each other.

I set them up as follows:

ATM2 (OK) (I want to keep the speaker on constantly during testing to hear everything)
ATX4 (OK) (I want them to report EVERYTHING to the Terminal window, as well as wait for dial tone, detect busy)
ATS0=1 (OK) (I want them to answer on the first ring)

So then I issue the ATDT1413267XXXX <CR> and the one I've issued that to dials away. The other line rings, and the other modem picks up, first ring just like I told it. The receiving modem does report RING to the Terminal window. And they start whistling, then hissing just like I would expect.

But neither ever reports CONNECT. And after a couple of seconds of hissing, I get a long, solid tone on the answering modem that sounds like a 1k square wave or something. It persists even if I disconnect the originating modem entirely. It only goes away if I manually issue an ATH to the answering modem that's making the tone.

I figured it out - the originating modem was timing out too quickly, the connection was taking longer and apparently the first modem was impatient. The tone is apparently the receiving modem saying "where the he$# did you go???"

Now, I am connecting just fine (CONNECT 9600) but when I send text from either terminal, it does not get echoed to the other modem's Terminal window.... I think I've had it for tonight, back at it tomorrow, maybe I'll be enlightened over night, or wake up to intelligent commentary on here :)

Thanks,

Dave

Comments

  • SapphireSapphire Posts: 496
    edited 2014-09-07 19:15
    Are the two modems same make/model/brand? If not, they are having a problem negotiating a common protocol. Try downrating the modem for your test. Issue an AT&N6 for 9600 bps. Also set AT&K0 to disable error correction for testing. There may be other settings you need to make, like ATS36=1 to force negotiation at a specific low rate, often called fallback (this may be modem specific). This speeds up the connection process considerably.

    Do you have the complete AT command set for your modems? Once you figure out the correct settings, save them in one of the profiles with AT&W# (where # is a number, usually 0-3). You can recall them with an AT&F# command.

    Here is a common command sequence I use for my stamp controlled modems. Note that parameters with a 0 (zero) are omitted (i.e. M0 is just M)
    SEROUT TD,MBAUD,["ATELMV&C1&D2&Q",CR] ' initialize modem
  • xanatosxanatos Posts: 1,120
    edited 2014-09-07 19:34
    Not the same modems - one is a modem from the previous century... literally. Works great, but I think the issue may actually be with the TinyModem. Check this little thing out: http://www.radi.com/modular51.htm I think the TinyModem - definitely from this century - comes set up on power-up in "voice data" mode, rather than in just straight data mode. So it's interpreting the data string I am sending as something to be played over the speaker at the receiving end. this is just a guess. I just downloaded the Voice Data addition set to the AT command set and will try that tomorrow. Everything in Command Mode works great for both modems, so I'm guessing that the issue is the Voice vs Data, Data Mode. The TinyModem also has a few different Fax modes as well. No documentation on how it comes set up by default.

    I'll report on my discoveries tomorrow.

    Thanks,

    Dave
  • SapphireSapphire Posts: 496
    edited 2014-09-07 19:41
    Dave,

    Okay. Keep us posted on how that TinyModem works with a "real" modem :)
  • msrobotsmsrobots Posts: 3,709
    edited 2014-09-07 19:47
    Dave,

    that long monotone tone on the receiving modem tells you that the connection is lost. It comes from the telephone company. Maybe them do not like analog modems anymore. Disturbing their digital system?

    The prove is that you can disconnect the originating modem and the tone persists. It's from the Telephone Cooperation, not the originating modem.

    ATH on the receiving end will hang up local and end this noise. Make sense?

    My guess is that the telephone line(s) you are trying to send analog signals thru are already digital and MAY not support 56K modems anymore.

    Or the modems are not compatible to each other. Not unusual at that time. 56K over old analog lines was often a problem.

    Two different steps to try.

    1. try to connect with 9600 baud. That should run fine even over digital lines and with different modems.
    2. find some old analog 'house-phone' system or how you call them in English. Nebenstellenanlage in German. One of those things you could install at your home (or small office) to phone from one home phone to the other. Then you can check if your modems are working like you want to without going over public phone lines. Look at yard sales. Old stuff.

    My personal GUESS here is that since landlines are not really landlines anymore, but get redirected to VOIP at the Tel.Co. anyways - 'high-speed' modems like 56K will not find the bandwidth and analog behavior on the VOIP line anymore. Like analog records for music (remember HiFi?) compared to MP3. Sound gets digitalized and dithered nowadays over the phone line. An them analog 56K modems might not be able to handle that anymore.

    just my 2 cents

    Mike
  • xanatosxanatos Posts: 1,120
    edited 2014-09-08 17:27
    It's all working. Terminal doesn't display the data after the modem switches from command mode to data mode, but RealTerm does. The data IS transmitted... it's all about the terminal emulator you're using. RealTerm is a pain in the $41 $53 $53 to set up, but it has its benefits... like reporting ASCII received in Data Mode after Command Mode has been exited.

    Thanks for your input folks. And the TinyModem is really nice. Not much bigger than the RJ11 jack itself, it is a truly fully-functioning data/fax/voice modem. Retails for $59.99 in single quantities. And modems are not dead! They just moved into the embedded systems arena. Think about it. Not all locations have wired or wireless internet; not all customers want to pay a monthly cellular tab; but almost every location has an analog phone line floating around, and a nice little 56k analog modem costs NOTHING every month to have it call out to send a little packet of data. The biggest data packet I might need to send, at 9600 baud, would take about 8 seconds to send. Modems still have their place. And they're fun! :)

    Dave
  • trookstrooks Posts: 228
    edited 2014-09-09 16:02
    During my research I seem to remember a number of RF 'modems' capable of much higher data rates than 9600 baud.

    My main interest in the XBee modules was to use them for communicating among a number of units.

    Somewhere out there is a 56K DSL modem on a chip that is also Mil Std. Anyone know where I can find them?

    Tim
  • xanatosxanatos Posts: 1,120
    edited 2014-09-09 16:13
    Hi Trooks,

    That DSL on a chip sounds interesting to me as well.

    I have to use a 56k modem for this app to communicate with a pre-existing data center. They want Telephony, Cell SMS and TCPIP connectivity all as available options.

    I love XBees. I have around 50 of them operating in teh field now in various applications. Mostly the XBee Pro XSC 900 mHz... rated 15 mile LOS, which means they're good for about 1/4 mile in real life :)

    Dave
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