Does anyone have docs for a Ventel brand MD212-plus modem?

Ethan Dicks ethan.dicks at
Wed Jan 11 02:05:42 CST 2017

On Sat, Dec 3, 2011 at 12:29 PM, Ethan Dicks <ethan.dicks at> wrote:

(Boosting the signal - look at the date on the original request...)

> A friend of mine just returned a modem he got from me decades ago, a
> Ventel MD212-plus.  It's an early-1980s non-AT-command-set
> autodialling modem.  The settings are adjusted via a pair of 10-pin
> DIP switches accessible from the back.  I've checked the web and
> bitsavers.  So far, all I've found is some old Usenet articles and a
> couple of pictures, but no manual or jumper guide.

So another friend gave me a Ven-Tel MD212-plus last year.  I am still
unable to cough up any docs online with the exception of the purpose
of switch H1 - it's the pulse-dial/tone-dial switch.  The other 19
switches remain mysterious.  I have done a bit of circuit tracing of
the main connectors (DB25 for EIA comms, DA15 for phone line/possibly
diagnostics) and the jumper positions on the mainboard (3 boards
inside - top one analog, middle one MCU and support chips and a lot of
CMOS, bottom one PSU+NVRAM battery+more analog).  Most of the
important serial settings are done on the dip switches.  The MCU
program has an interactive menu system for adding numbers to the
onboard NVRAM (appears to be an RCA5101 256x4 CMOS SRAM kept alive
with a CR2430 lithium coin cell) and dialing from the NVRAM or
interactively.  This was a great modem for sticking on a VT100 and
interactively dialing into work.  It was not a great modem for UUCP
because it had a screwy menu system with timings that were expecting a
human poking keys not software blasting out commands.

Front View:

Rear View:

Front Panel LEDs:

MB | TR | MR | SD | RD | HS | MC | TM

Front Panel pushbutton switches:
AL | ST | RDL | DL | HS

ISTR HS is the 300 baud/1200 baud switch.  RDL and DL should be
loopback test buttons.  AL could be analog loopback.  Don't recall off
the top of my head what ST might be.

There is very little technical detail online about this modem.  The
vast majority of hits are people asking for a manual or jumper
settings.  I may have some documentation on an ancient backup tape
from the 80s but nothing has surfaced in the past 5 years.  Sadly, I
have misplaced the one DA15->4p4c phone cable I had.  No idea what
sort of internal connections/passive components may have been on the
DA15 plug but one presumes that the red and green wires from the
modular jack went into 2 of the pins on the DA15.  Tracing out the
entire DA15 revealed some curious stuff, including that very few of
the pins were no-connects.

If anyone happens to have a cache of 1980s modem docs, perhaps
something will surface.

Internally, here's what I found after an hour of poking around:

F10 - 10-pin DIP switch
 F1 ?
 F2 ?
 F3 ?
 F4 ?
 F5 ?
 F6 ?
 F7 ?
 F8 ?
 F9 ?
F10 ?

H10 - 10-pin DIP switch
 H1 Pulse Dial (up) / Tone Dial (down)
 H2 ?
 H3 ?
 H4 ?
 H5 ?
 H6 ?
 H7 ?
 H8 ?
 H9 ?
H10 ?

J1 DB25
 1 Protective Gnd (JP5)
 2 RxD
 3 TxD
 4 CTS
 5 RTS
 6 DSR
 7 Signal Gnd
 8 DCD
 9 Data set testing?
10 Data set testing?
11 NC
12 SDCD (JP1)
13 SRTS (NC)
14 STxD (NC)
15 DB/TCLK (sync transmit clk)
16 SRxD (NC)
17 DD/RCLK (sync receive clk)
18 LL (NC)
19 SCTS (NC)
20 DTR
21 RL/SQ (NC)
22 RI
23 CH/CI?
25 TM?

J2 - DA15
 1 NC
 2 NC
 3 J3 pin 26
 4 J3 pin 25
 5 to F10 DIP SW ?
 6 Gnd
 7 J3 pin 20 ? (to be verified)
 8 J3 pin 18 ? (to be verified)
 9 J3 pin 5
10 +5 / VCC ? (to be verified)
11 J3 pin 15 Vee / -12V
12 NC
13 NC
14 JP4 pin 3 (open)
15 JP3 pin 3 ? (open)

J3 26-pin 0.1" header between digital/MCU board and PSU board

[ When I used to use these modems on a daily basis, we never opened
them up and fiddled with these jumpers, but I'm including my findings
for completeness ]

JP1 3-pin with jumper on 1-2
 1 B9 pin 6 (1488)
 2 J1 pin 12 (DB25 connector) SDCD
 3 NC

JP2 3-pin with jumper on 1-2
 1 1489 @ C9 pin 1
 2 DB25 pin ?
 3 1489 @ C9 pin 10

JP3 3-pin, no header installed, pin 1-2 jumper on PCB
 1 J3 pin 12
 2 J3 pin 12
 3 J2 pin 15 ? (to be verified)

JP4 3-pin, no header installed, pin 1-2 jumper on PCB
 1 J3 pin 11
 2 J3 pin 11
 3 J2 pin 14 (DA15 connector)

JP5 2-pin, header and jumper installed
 1 GND
 2 J1 pin 1 (DB25 connector)

JP6 3-pin, no header installed, pin 1-2 jumper on PCB
 1 +5V/Vcc
 2 ? - via under 8039 MCU @ F/H 4
 3 Gnd

JP7 3-pin, no header installed, open
 1 Gnd
 2 P8243 MCS48 I/O expander @ H 7/8 pin 1 (P50) with pullup to Vcc
 3 NC

JP8 2-pin, no header installed, open
 1 ? with pullup to Vcc
 2 Gnd

JP9 2-pin, no header installed, open
 1 ? with pullup to Vcc
 2 Gnd

JP10 2-pin, no header installed, open
 1 ? with pullup to Vcc
 2 Gnd

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