9 Oct
2025
9 Oct
'25
5:34 p.m.
I was poking around eBay and up came a listing for a DEC "mini exchange", DFMSA.
What is that? The name doesn't sound familiar. It looks like a box with a bunch of
DB25 connectors on the back, but that doesn't help much.
paul
9 Oct
9 Oct
6:09 p.m.
I was poking around eBay and up came a listing for a
DEC "mini exchange",
DFMSA. What is that? The name
doesn't sound familiar. It looks like a box with
a bunch of DB25
connectors on the back, but that doesn't
help much.
See page 4.50 of
https://bitsavers.trailing-edge.com/pdf/dec/catalog/Digital_Networks_and_Com
munications_Buyers_Guide_198710.pdf
From that page:
The Mini-Exchange is a microprocessor-based, standalone, asynchronous
circuit
switch designed for local connection of up to eight of Digital's personal
computers (DECmate II, Rainbow personal computer, and Professional 300
series). It operates at speeds of up to 19,200 bits per second. Modem
control is
offered on line eight only. The Mini-Exchange offers DCS product support for
file transfer operations to IBM PC/XT, Apple II and III, and TRS-80 systems.
The Mini-Exchange is the least costly method of connecting personal
computers
and associated devices within a 60 meter (200 foot) area. It provides
flexibility in designing local hardware configurations and allows
asynchronous
communications to other Mini-Exchanges for host systems over modems.
7:57 p.m.
On Thu, Oct 9, 2025 at 2:57 PM Ron Pool via cctalk
<cctalk(a)classiccmp.org> wrote:
I think I have one of these. I fiddled with it when I first got it,
but haven't had a reason to pull it out recently.
From what I recall, you sent specific control codes either from some
sort of hot-F-key memory or by using DOS utilities like XATTACH and
XDETACH to switch ports (I never fiddled with the DOS utilities). It
could be interesting to use as an async traffic switch for file
transfer programs like Kermit, I don't remember how many simultaneous
connections it supports.
Here's a usage manual I pulled up after a quick search.
http://www.bitsavers.org/pdf/dec/rainbow/ms-dos/AA-DY84A-XV_Rainbow_Using_t…
Cheers,
-ethan
I was poking
around eBay and up came a listing for a DEC "mini exchange",
DFMSA. What
is that? The name doesn't sound familiar. It looks like a box with a bunch of DB25
connectors on the back, but that doesn't help much.
See page 4.50 of
https://bitsavers.trailing-edge.com/pdf/dec/catalog/Digital_Networks_and_Com
munications_Buyers_Guide_198710.pdf
From that page:
The Mini-Exchange is a microprocessor-based, standalone, asynchronous
circuit switch designed for local connection of up to eight of Digital's personal
computers... 
6:24 p.m.
On 2025-10-09 13:34, Paul Koning via cctalk wrote:
I was poking around eBay and up came a listing for a
DEC "mini exchange", DFMSA. What is that? The name doesn't sound familiar.
It looks like a box with a bunch of DB25 connectors on the back, but that doesn't help
much.
paul
I had one once. AFAIR it is just a serial switch to access different
peripherals from one port on the CPU. Possibly switchable by control
sequences. That was 35 years ago though so I am not sure of setails!
cheers
Nigel
--
Nigel Johnson, MSc., MIEEE, VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
We started the Maker-Mender Movemnt a hundred years ago!
8:07 p.m.
On Thu, Oct 9, 2025 at 12:32 PM Nigel Johnson Ham via cctalk <
cctalk(a)classiccmp.org> wrote:
On 2025-10-09 13:34, Paul Koning via cctalk wrote:
http://www.bitsavers.org/pdf/dec/rainbow/ms-dos/AA-DY84A-XV_Rainbow_Using_t…
tells how to use it with a DEC Rainbow. So all the ports are RS-232. It
was used to share Printers and modems to the Rainbow (though modems had
weird restrictions iirc). I don't know if the protocol has been
reverse-engineered (likely it has), but the MS DOS 2.11 programs are small.
Warner
I was poking around eBay and up came a listing
for a DEC "mini
exchange", DFMSA. What is that? The name doesn't sound familiar. It
looks like a box with a bunch of DB25 connectors on the back, but that
doesn't help much.
paul
I had one once. AFAIR it is just a serial switch to access different
peripherals from one port on the CPU. Possibly switchable by control
sequences. That was 35 years ago though so I am not sure of setails!
8:30 p.m.
Didn't it allow DECnet/DOS over serial lines, too?
Warner Losh via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 9. Okt.
2025, 22:17:
On Thu, Oct 9, 2025 at 12:32 PM Nigel Johnson Ham via
cctalk <
cctalk(a)classiccmp.org> wrote:
On 2025-10-09 13:34, Paul Koning via cctalk
wrote:
http://www.bitsavers.org/pdf/dec/rainbow/ms-dos/AA-DY84A-XV_Rainbow_Using_t…
tells how to use it with a DEC Rainbow. So all the ports are RS-232. It
was used to share Printers and modems to the Rainbow (though modems had
weird restrictions iirc). I don't know if the protocol has been
reverse-engineered (likely it has), but the MS DOS 2.11 programs are small.
Warner
I was poking around eBay and up came a listing
for a DEC "mini
exchange", DFMSA. What is that? The name doesn't sound familiar. It
looks like a box with a bunch of DB25 connectors on the back, but that
doesn't help much.
paul
I had one once. AFAIR it is just a serial switch to access different
peripherals from one port on the CPU. Possibly switchable by control
sequences. That was 35 years ago though so I am not sure of setails!
8:45 p.m.
I have a PC XT set up to be on a VMS cluster from this era.
b
On Thu, Oct 9, 2025 at 4:37 PM Hans-Ulrich Hölscher via cctalk <
cctalk(a)classiccmp.org> wrote:
Didn't it allow DECnet/DOS over serial lines, too?
Warner Losh via cctalk <cctalk(a)classiccmp.org> schrieb am Do., 9. Okt.
2025, 22:17:
On Thu, Oct 9, 2025 at 12:32 PM Nigel Johnson Ham
via cctalk <
cctalk(a)classiccmp.org> wrote:
http://www.bitsavers.org/pdf/dec/rainbow/ms-dos/AA-DY84A-XV_Rainbow_Using_t…
On 2025-10-09 13:34, Paul Koning via cctalk
wrote:
I was poking around eBay and up came a listing
for a DEC "mini
exchange", DFMSA. What is that? The name doesn't sound familiar. It
looks like a box with a bunch of DB25 connectors on the back, but that
doesn't help much.
paul
I had one once. AFAIR it is just a serial switch to access different
peripherals from one port on the CPU. Possibly switchable by control
sequences. That was 35 years ago though so I am not sure of setails!
tells how to use it with a DEC Rainbow. So all
the ports are RS-232. It
was used to share Printers and modems to the Rainbow (though modems had
weird restrictions iirc). I don't know if the protocol has been
reverse-engineered (likely it has), but the MS DOS 2.11 programs are
small.
Warner
7
days inactive
7
days old
6 comments
7 participants
participants (7)
-
amp1ron＠gmail.com -
Bill Degnan -
Ethan Dicks -
Hans-Ulrich Hölscher -
Nigel Johnson Ham -
Paul Koning -
Warner Losh