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Old 5th Mar 2015, 11:39 am   #1
Dave Moll
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Default Amstrad SM2400 modem

Thanks to a forum member I recently acquired an Amstrad SM2400 modem.

I am currently trying to put this to use for data communication between two extensions of my in-house PABX, but I have no information on control of this modem. The function I am currently looking to achieve is making it sieze the line - either to auto-answer an incoming call or to dial an outgoing one. Currently, the incoming ring current causes a brief flash of the "ring detect" light on the modem on each ring, but no other action.

There may be further hurdles to overcome (such as ensuring that there is a match of baud rates throughout the system) once I've achieved this first stage, but I'll save those until I get over this first one.
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Old 5th Mar 2015, 11:58 am   #2
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Default Re: Amstrad SM2400 modem

From a quick Google, it seems that the SM2400 does support the 'AT' command set so you need it connected to a computer to get it to do things. Connect the serial port to a PC using an appropriate cable, or USB-serial adapter, and set the PC's baud rate to 9600 baud (that usually works for me - note that it's independent of the baud rate the modem sends over the phone line). If you type AT and hit return, the modem should respond with AT. If it doesn't, you'll need to play with the baud rate and serial cable wiring. Modem cable wiring is notoriously painful to get right - do you have a cable already?

To get it to dial, type ATD<phone number> followed by return, for example ATD12345. When the line is ringing with an incoming call, it'll probably send RING to the PC, and you can type ATA then return to answer the call.

There are also a myriad of various settings to set up auto-answer and so on. The Wikipedia page is a good starting point for the command set:
http://en.wikipedia.org/wiki/Hayes_command_set
but bear in mind that the SM2400 is sufficiently old that some features may be non-standard or unsupported.

Good luck!

Chris
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Old 5th Mar 2015, 11:59 am   #3
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Default Re: Amstrad SM2400 modem

Most modems of that era used the Hayes command set: http://en.wikipedia.org/wiki/Hayes_command_set

(Chris beat me to it )
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Old 5th Mar 2015, 1:01 pm   #4
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Default Re: Amstrad SM2400 modem

Thank you both. Ah yes, Hayes does now ring a vague bell (if you'll excuse the pun) now that you mention it. I shall give these a try and report back.
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Old 5th Mar 2015, 3:38 pm   #5
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Default Re: Amstrad SM2400 modem

You probably will want to make yourself up a tester with a bi-colour LED (or two LEDs wired back-to-back) and a series resistor of a few kΩ. This will help you determine which pins on which connector are driven.
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Old 5th Mar 2015, 4:11 pm   #6
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Default Re: Amstrad SM2400 modem

Brilliant! Communication has now been established between a Pentara Plus and the PDS software running on an IBM PC/AT - and the Pentara's database successfully copied to floppy disc. Any problems encountered within that exercise are beyond the scope of this thread.

Many thanks; problem solved.

edit: actually, AJS, I was monitoring the lines with the gadget shown below:
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Last edited by Dave Moll; 5th Mar 2015 at 4:16 pm.
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Old 6th Mar 2015, 9:29 am   #7
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Default Re: Amstrad SM2400 modem

Great! I'm glad to hear it worked. Nothing wrong with 2400bps if it gets the job done.

Chris
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Old 6th Mar 2015, 3:22 pm   #8
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Default Re: Amstrad SM2400 modem

Actually, the task it's doing is limited by other parts of the setup to 1200 at most.

One thing I haven't yet fathomed is that I can't seem to get it back into command mode (with "+++") to send it an "ATH" to clear down afterwards. I'm currently taking the somewhat brutal approach of disconnecting from the modem, but hey, it gets the job done!
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Old 6th Mar 2015, 5:20 pm   #9
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Default Re: Amstrad SM2400 modem

You have to type the characters very quickly if you're typing them manually. Just pulling the plug out or powering the modem off will have exactly the same effect of course, so nothing to worry about.
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Old 6th Mar 2015, 6:08 pm   #10
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Default Re: Amstrad SM2400 modem

Actually, I have them stored in a file that I copy to COM1:
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Old 9th Mar 2015, 6:38 pm   #11
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Default Re: Amstrad SM2400 modem

You need a delay after the +++, apparently, or it gets sent as data !

Glad to hear it all works.

dc
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Old 9th Mar 2015, 7:28 pm   #12
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Default Re: Amstrad SM2400 modem

The problem I was encountering was that any attempt to copy a command file to COM1: once a connection had been established gave a message along the lines of "write error on COM1:". I had a batch file containing the following:

COPY PLS.TXT COM1:
PAUSE
COPY ATH.TXT COM1:

... where PLS.TXT contained the string "+++", and ATH.TXT contained the string "ATH". I received the error message immediately on processing the first COPY command.

Unfortunately, I shall have to put this exercise on hold for the present, as the monitor of the PC-AT I was using decided to pack up this afternoon.
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Old 16th Mar 2015, 3:32 pm   #13
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Default Re: Amstrad SM2400 modem

First I had better say that the monitor problem turned out to be purely temporary. When I got it on the operating table and removed its case, I powered it up to start checking voltages and found that it was back in working order - and has continued to be ever since. I can only assume that it had overheated, as I had inadvertently left a manual on top of it, and a thermal cut-out had operated. The investigations therefore continue.

I haven't made any further progress in getting the "ATH" command accepted, but have inadvertently found a way of causing the modem to hang up - by attempting to set the communiction speed to 300 baud. Needless to say, this wasn't the result I was looking for!

The modem describes itself as "quad speed" - which I had assumed meant that it could run at 2400, 1200, 600 or 300. I have been running it successfully at 1200 to communicate with my Pentara PABXes, but there are a couple of exercises I want to try that require 300 baud operation. Does anyone know what speeds the modem supports?
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Old 16th Mar 2015, 3:48 pm   #14
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Default Re: Amstrad SM2400 modem

Quad speed does normally mean what you suggest. The two modems normally negotiate to determine the highest speed which both will support.

Why would you want to force 300 if both ends support a higher speed?
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Old 16th Mar 2015, 4:34 pm   #15
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Default Re: Amstrad SM2400 modem

Although I have hit the problem with modems that can both work at higher speeds than 300, I was trying to establish that communication was possible at 300. What I was roiginally trying to do with the 300 baud communication was to converse between the SM2400 and the internal modem of the Pentara which is only 300 baud - which was dropping the link as soon as the Pentara transferred the call to its modem.

The other exercise I want to try at some stage, though the equipment to do so is not easily accessible at present, is to establish communication with an acoustic modem I have - which I believe also requires a 300 baud link.
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Old 16th Mar 2015, 6:34 pm   #16
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Default Re: Amstrad SM2400 modem

They should negotiate down to 300 without your having to do anything.
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Old 16th Mar 2015, 8:22 pm   #17
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Default Re: Amstrad SM2400 modem

OK. I'll work on the assumption that the Pentara-related problem is not the fault of the SM2400 - thus outside the remit of this thread.
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Old 16th Mar 2015, 8:38 pm   #18
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Default Re: Amstrad SM2400 modem

There are no guarantees - this modem is 30 years old and was pretty cheap'n'cheerful when it was new. I obviously have no idea if it's working properly, or if it worked properly in the first place. However, I think I've described what it should be doing.

Low end modems like this were mostly used to communicate with commercial dialup providers who were using expensive professional kit. These would have been at least one generation ahead, so nobody put much effort into confirming that domestic modems would negotiate down properly. Almost everyone would want to use them at their maximum possible speed.
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Old 16th Mar 2015, 11:07 pm   #19
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Default Re: Amstrad SM2400 modem

Dave just sent you a PM I have a professional modem you can have FOC

Jay
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Old 16th Mar 2015, 11:19 pm   #20
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Default Re: Amstrad SM2400 modem

PM reply sent.
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