[fa.info-vax] DZs vs. DMFs

info-vax@ucbvax.ARPA (10/15/84)

From: "Brand Hal"@LLL-MFE.ARPA

   A piece of trivia that hopefully might save someone else some time and
money (now that I've lost mine).   Our 750 is located across the street, so
we needed to run RS422 to the offices.   We choose to use Black Boxes in the
individual offices, but wanted something more compact (and less expensive)
at the 750 end.   We choose an MDB distribution panel designed for their
(or DECs) DZ (equivalent) that provided both RS-232C and RS-422 output.   This
solution had been working fine for a 780 already in place using DEC DZs and
Able VMZs.   However, when we tried using the MDB box with our DMF, no good.
The computer could send, but didn't receive at all.   We then tried just movig
(moving) the RS-232 connector from a DMF port to a DZ port and then everything
worked.   Upon checking the output of the MDB box back to the 750, we
discovered that it was only generating TTL levels (0 and 5 volts).   The
DZ is happy with this, but the DMF is NOT.   As best I can read prints, the
DMF has a -9.9 volt "pull-down" on the RS-232C receive line, thus 5 volt
swings just won't cut it.   Anyway, the moral of the story is:
Just because it works with a DZ, doesn't mean it will work with a DMF.   I
suspect that a similar problem might be encountered when running RS-232C over
long distances.
   Finally, does anybody know of a real commercially available RS-232C to
RS-422 converter for 8 or more lines (perferably rack mountable)???

info-vax@ucbvax.ARPA (11/25/84)

From: hplabs!kaist!chon@BERKELEY (Kilnam Chon)

 Chon

info-vax@ucbvax.ARPA (11/25/84)

From: sasaki@harvard.ARPA (Marty Sasaki)

Aren't DEC DMZ's supposed to support 24 lines? DMF operation? full modem
control on all lines?

			Marty Sasaki
			Harvard University Science Center
			sasaki@harvard.{arpa,uucp}