Modems and external dialers.

[Ethan Dicks]

On Tue, Jun 4, 2019 at 9:45 PM Grant Taylor via cctalk
<cctalk at classiccmp.org> wrote:
> Does anyone have any experience working with modems that didn't include
> internal / auto dialers?

Yes.  I used to make and sell sync serial protocol engines (COMBOARDs)
that often were used to dial up an IBM Mainframe.  Sync modems of the
80s often did not have built-in auto-diallers.

Here's one we used to use, a Motorola UDS 801 ACU (Automatic Call Unit).

http://nwrusa.com/Networking?product_id=17371
https://www.arcelect.com/801_autodialer.PDF

I still have one on a shelf in the basement.

> I think they were separate devices, which probably means that they
> likely had separate serial ports to talk to each of them.  Did they
> support some sort of pass through?  Or did they really require two
> serial ports on the host?

Yes (though the USD 801 ACU could be controlled by a parallel port
_or_ a serial port)  In our case, our product had a sync serial port
to talk the the Host (implemented with either a COM 5025 or a Z8530).
To run the 801 ACU, we soaked up an async port on the VAX as well.

Sometime after 1990, I added V.25bis support to our product so we
could control autodialers of the day.

-ethan