cetron%utah-ced@UTAH-CS.ARPA (Ed Cetron) (12/06/86)
I received the following request:
From: K. Sankara Rao
<NU043109%NDSUVM1.BITNET@WISCVM.WISC.EDU>
Subject: Microvax and modem interconnect problems
Dear Ed:
We here, in Electrical Engg. Department of North Dakota
State University have a MicroVAXII running under VMS 4.4. There is
a Gandolf PACX network in the University and we want to connect the
MicroVax to it with full modem control. THe port controllers are DHV-11.
That is where the trouble started.
When the port is set as a MODEM: as soon as somebody
comes on to the line, in exactly 30 seconds time, the system logs
him off with an error SYSTEM - E - HANGUP massage. What seems to be
happening is this. For some reason, DTR from the line is dropped for
a short duration (We cannot see it happening with leds) and as a
consequence, the PACX swith drops (again for a short duration)
either DSR or Carrier signal and the system senses a line hangup
and logs the terminal off. Have you ever heard of any such problems
before and can you suggest a solution?
At present we are using the uVAX on the PACX seeting
the ports as NOMODEM and we do not have any modem control (like
the process being deleted if the line drops, i.e, a user forgetting
to logout before switching the line off) and this is not a 'safe'
solution.
Thanks in advance.
Rao
Department of EEE
NDSU, Fargo, ND 58105
Tel : (701)237-7217
no problem, I've read the dhv-11 manual....it says:
dhv-11 will assert RTS and DTR all of the time when /modem
then the modem should raise RI
then pause
then raise DSR indicating phone line connection established
the raise DCD when carrier is established
then raise CTS when ready to transmit/receive
so I wrote back:
I thought the answer was the following:
vax brings up dtr and rts
modem brings up dsr (and maybe ring if needed)
pause by modem to establish carrier
modem brings up carrier detect AND CTS
vax no allows you to speak to/from it just fine
if you don't login completely within 30 seconds (or whatever you have set in
sysgen), vax will lower dtr for 4 seconds, then lower rts also, then
raise them both after 1-2 seconds...
empirical data:
our one system with an able mux master works just fine now when we brin
g up cts with cd. but would do exactly what you describe except the error was
file read error when we didn't raise cts...
-ed cetron
BUT!!!!!
before i sent this, I tried to verify this on my real dhv-11.... I set the
line /modem/hangup/dialup/disconnect/perm, forced my breakout box (pretending
it was the modem) to hold cd, cts, and dsr low. I then connected a terminal
to tx and rd and tried it. IT WORKED!!! but its not supposed to....no till
I raise cd, cts and dsr....I am sooooo..... confused......
Did I set something wrong????, is the dhv-11 brain-damaged???
and I thought I understood the way dec handled modem control.....Before I
start reading the fiche, does anyone understand what is happening????
-ed cetron
(sorry for the length)
s