Modems and external dialers.

[Ethan Dicks]

On Wed, Jun 5, 2019 at 10:42 AM Grant Taylor via cctalk
<cctalk at classiccmp.org> wrote:
> Reading the links that Ethan provided, it sounds like some auto-dialers
> did use a second port, but it was not a second (recommended) standard
> 232 port.  Instead it was an RS-232 and RS-366.
>
> Aside:  RS-366 sounds odd.  A combination of serial signaling and
> parallel signaling on the same port.  But not the same as a traditional
> parallel printer port.

Not quite... the USD 801 ACU I keep mentioning supported dialing using
either RS-232 or RS-366 over the same physical port.  It was a
flexible device that would work with a parallel dialing controller
like the DEC DN11 or by just using a second serial port from your
host.

> > My first modem was a box about 12x8x2.5 inches and it was an all analog
> > modem good for 110/300 baud and it required connection to the phone line...

My own first modem (vs the sync stuff I've been mentioning) was a
Commodore VICmodem that didn't even connect directly to your phone
line that I got in late 1982.

The host connector was a TTL-level edge connector for the VIC-20/C-64
User Port.  There were routines in ROM that emulated a 6850 ACIA for
Kernel device #2 (OPEN 2,2,2...) but from an application software
standpoint it worked just as if you had a UART in the machine.  The
other connector was a handset connector for a standard US telephone
(narrow 4p4c jack).  Internally, the modem was functionally like a
Novation Cat without the acoustic cups or the EIA level converters or
indicator LEDs.

To use this modem, you'd load and run your terminal app then pick up
the phone and dial the number.  When the far end answered, you'd
unplug the coiled cord from the handset and quickly plug it into the
VICmodem before the other end hung up.  It did have the advantage over
an acoustic coupler in that room noise was not a factor and it had the
advantage over a Hayes modem of cost (ISTR the VICmodem was somewhere
around $70 and did not require the $50 Commodore RS-232 "interface"
(analog level shifter with DB25 port).  I did eventually get that
RS-232 cartridge but not for modem work.  I got it to hook my C-64 to
other local machines for file transfer.

Like a lot of hobbyists in the 70s and 80s, I spent a lot of time
making serial adapters and debugging serial comms.  It came in handy
when I went to work for the place that made sync serial devices.  I
still do most of my hacking on a Dell laptop that's old enough to have
a real serial port and I do use that port.  It has advantages over USB
dongles for some of the less-traditional uses (like 45.45 / 50 bps and
2 stop bits for old teletypes).

-ethan