🚀 go-pugleaf

One of the researchers down the hall recently acquired a Masscomp 55S.
(Or is it a 5500S?  The purchase order and the tag on the back of the
CPU box use the former designation, whereas the maintenance agreement
uses the former.)

Whichever, there is a weirdness with the serial ports, which Masscomp
hasn't yet given us an answer to:

Needing dialin access, we hooked up a standard modem to the "REMOTE"
port, and succeeded in dialing in once.  Following that, things would
no longer work:  The modem would answer, but immediately drop carrier.
After a bit of poking around, we found that the Masscomp's REMOTE port
had something odd on its DTR line:  A perfect square wave, amplitude
10V, period approximately 9.174 KHz.  No wonder the modem was confused!
There was also a nice square wave, amplitude 8V, period approximately
292.4 Hz, on the "LOCAL" port.  The "PRINTER" port looked fine.

The field service person arrived, and swapped the CPU board.  (As to
*why* Masscomp would design a system that requires that the CPU board
be swapped when a serial port goes out to lunch is another question.)
This fixed the problem.  But, unfortunately, the problem reappeared as
soon as we dialed in again!  The modem<=>computer cable connects the
standard RS232 pins: 2,3,4,5,6,7,8,20,22.  I suspect that there may
something nonstandard about Masscomp's serial ports, and that perhaps
transition from -10V to +10V (or vice versa) on pin 22 ("RING") breaks
something.  Of course, there is nothing in any of the documentation
that we received that tells you which pins they *want* connected when
you hook a modem up to the "REMOTE" port.

Masscomp, of course, seems reluctant to keep swapping CPU boards, only
to have them break again.  But on the other hand, we know it's not the
modem's fault.  We could proceed by trial and error (e.g. as a first
attempt, try not connecting pin 22), but I suspect that someone must
have already encountered this problem.  Does anyone have a quick and
ready answer?  Thanks in advance.

---

Mark Bartelt                          UUCP: {utzoo,decvax,ihnp4}!sickkids!mark
Hospital for Sick Children, Toronto   BITNET: mark@sickkids.utoronto
416/598-6442                          INTERNET: mark@sickkids.toronto.edu

[ Note: The internet address is claimed to work, but has not yet been tried. ]