"party line" for terminals?
john3000 at cox.net
Fri Mar 17 23:54:37 CST 2006
Sounds like the old HP "MultiPoint" terminal configuration we used for a
while at George Mason University. I don't remember the exact years, but it
was probably 1978, 1979, or 1980. IIRC used a Sync 9600 circuit between
the devices. You put a sync card in the HP 2645 terminal instead of the
async card and I think there was some external media adapter too. I
remember working with an HP SE named Tom Benedict out of the Rockville, MD
office to try to get our multipoint setup to work in a reliable
fashion. The problem was that turning any terminal in the chain off shut
down the entire chain, and a hard reset really messed it up as well.
We eventually removed the sync cards from the 2645 terminals, went async,
and used twisted pair to connect the HP 2645 terminals. Because of the "50
foot" limit on RS-232, we were an "unsupported configuration" because we
had anywhere from 700+ feet to over 2500 feet of twisted pair between the
HP 3000 Series III MUX ports and the HP 2645 terminals.
When some years later we added a HP 3000 Series 64 with ATP ports we found
that to log on we had to set the terminal speed to 2400 baud, log on, then
issue a SPEED 960,960 and switch the speed to 9600. We did that for a
couple of years until we installed a broadband cable system (IIRC I think
it was Sytek).
I don't know if Tom Benedict is still with HP, but at the time he was an
expert on the MultiPoint technology. I'm sure he would have some
interesting tales to tell.
Going way beyond the "Party Line" topic, does anyone remember the Sytek
system? The Sytek network used bidirectional CATV technology for the
backbone and network interfaces that used two Z80 processors to connect
RS-232 devices. One Z80 handled the RS-232 interfaces (you could have 1 to
8 19,200 bps RS-232 ports) and the other handled the
modulation/demodulation of the RF carrier. A 68000 Unix box acted as the
network control center (NCC). When you turned on a terminal and hit return
you got the attention of the NCC and it gave you a menu of available
devices (ones which you had permission to access ANDed with the devices
[systems] which had available ports). I know the Sytek system was used at
NASA, as it was through NASA that we found out about the Sytek "local area
network" equipment sometime about 1979 or 1980. With the CATV bandwidth
and the frequency spectrum divided up for various uses, the Sytek network
allowed a dozen or so video channels, a few thousand phone calls, and
several thousand 19.2 kbps terminal connections simultaneously on a single
cable. Not bad for late 1970's technology.
At 2006-03-17 06:04 PM, you wrote:
> > The HP264x terminals had something vaguely similar. You could daisychain
> > terminals off eachother in a bus configuration instead of the typical star
> > configuration (all RS232). MultiDrop I think they called it.
>Yes, but it was an option (a rarely seen option at that).
>I never saw one running.
>IIRC, it was a poll/select system, ala Burroughs early CRT terminals in
>the early 1970s.
>sieler at allegro.com
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