Serial problems on DecStations?
George Robbins
grr at cbmvax.commodore.com
Wed Feb 21 11:48:50 AEST 1990
In article <432 at wattres.UUCP> steve at wattres.UUCP (Steve Watt) writes:
> In article <6152 at umd5.umd.edu> hans at umd5.umd.edu (Hans Breitenlohner) writes:
> >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
>
> >Personally, I would consider anything that can not operate on +/- 5 Volts
> >broken. (I assume that is under load, not open circuited).
>
> Just curious: Does anybody know of an "RS232 signal booster" of some sort?
> Like where to buy one, or schematics or something?
Yes, you can get "RS232 Line Extenders" that are probably just an RS232
receiver and driver with a power supply. Black Box and others have them,
but you'd want to be sure they handle modem control and not just transmit/
receive signals.
You can do the same with some 1488's and 1489's from Radio Shack...
Note that the threshold voltage for 1489's can be controlled by a resitor
between the "response control" pin and one of the power supply rails. I'd
halfway suspect the modem is doing something like this to shift the threshold
to prevent no-connect "chatter", otherwise the threshold should be only a
volt or so...
--
George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr
but no way officially representing: domain: grr at cbmvax.commodore.com
Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)
More information about the Comp.unix.ultrix
mailing list