Serial problems on DecStations?

[Hans Breitenlohner]

In article <423 at wattres.UUCP> steve at wattres.UUCP (Steve Watt) writes:
>I have discovered why this doesn't work:  If you hang an oscilloscope off of
>the serial port on the DECStation 3100, you see a voltage swing of -5v to +5v
>!!!  I realize that this is "officially" allowed in RS232-C, (but not -D), but

And what does RS232-D specify for voltage levels?

Personally, I would consider anything that can not operate on +/- 5 Volts
broken.  (I assume that is under load, not open circuited).

The only time we have run into anything like that was with line drivers
which were powered from one of the control signals (DTR?), which failed
mysteriously when that signal was too low (though within RS232-C specs).

I would be surprised if your modem was powered from the interface, but 
if it is, it may be fairly easy to substitute a highere voltage on the
appropriate line.