Simulated telephone

Brent Hilpert hilpert at
Thu Aug 26 01:16:11 CDT 2010

On 2010 Aug 25, at 9:02 PM, Fred Cisin wrote:

> On Tue, 24 Aug 2010, Brent Hilpert wrote:
>> If both modems in a given connection are older ('80s), lower-speed
>> (300-1200/2400) it will likely work by simply connecting them together
>> and commanding one off-hook in answer mode (ATA ?), then the other
>> off-hook in originate mode (ATD ? ATH1 ?). I have successfully done
>> this with particular modems up to 14.4Kbps but might be forgetting the
>> commands.
> Many of my older modems are from BEFORE "Hayes Compatible" became the
> standard for giving commands to the modem.

Well, I was thinking of adding in that if you have a really old modem 
you might have to flip the originate/answer switch appropriately if it 
has one, but I think the OP indicated he was dealing with later stuff.

(I have a couple of pre-'smart' modems, too.)

> BTW, Joe Campbell ("RS232 Solution", "C Programmer's Guide to Serial
> Communication", etc.) got hired later by Hayes to document just what 
> the
> Hayes "standard" consisted of, because there were numerous variation in
> commands between Hayes' own modems!

The hayes command set always seemed non-sensical to me. For example, 
the AT prefix on (almost) everything when you were already in command 
mode seemed quite unnecessary.

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