Exploring the (now useless) Microcom Parallel Port Modem

[voidstar78]

I got an unopened Microcom DeskPorte FAST+ that is from early 1990s era (1993-ish, or at least pre-Win95 era since it only has Win3.x drivers).

The use-case seems to be that if you had an old system (say <10MHz) stuck with a ~1.8MHz clocked 8250-UART, you could use this "parallel port modem" to accelerate the system-to-modem speed. The serial card on the original 4.77Mz PCs were notorious for being limited to 9600 baud (but that was related to a bug in the original system BIOS). But there may be a set of other slow systems (e.g. early 4 or 8MHz x86 laptops) with a weak integrated UART that also couldn't muster past 9600 baud [ but were performant enough to run Windows 3.x ?? ]

I decided to see if it even worked and what I could do with it. This particular one uses 240VAC, which I happened to have an appropriate power adapter for that. And I happened to have an old 486 that still has WFW3.11 installed. After installing the Microcom driver and setup, it creates a "virtual COM port" (I initially set it to use COM8 and later easily changed that to COM4 with their config software), but this relays the data across the designated LPT port.

So for modem communication, it's two stages: the byte has to get tossed over to the modem, then the modem encodes that into an audio signal. So there are two bottlenecks: how fast the host system can toss the data over to the modem, and how fast the modem can encode the signal and squawk it out. It's often 1:1 but for older/slower systems, a "fast modem" could outperform the hosts' serial port. For a pre-PCMCIA laptop, it might be hard to upgrade its serial-port parts. Or for a slow corporate office desktop, they might not permit you to crack open its case. But if you didn't need a printer, you could hijack the parallel port to speed up the host-to-modem exchange with a "parallel port modem."



Per the Microcom manual, this parallel port modem has an "autobaud" feature - where as soon as you type in the terminal, it automatically figures out what your host system baud rate is. However my install of WFW3.11 Terminal program only let me set up to 19200 baud - I didn't get time yet to install an alternative terminal program (Procomm for Windows for example). But even with this, I was getting "OK" responses from this modem.


This modem does also have a serial connection also. So I was hoping there was some kind of "relay mode" between the parallel-port side and its serial-port side. If it did, then I imagined we could use this thing as a kind of "externally attached high speed serial port" on an old system - but so far I don't think it has a mode for that. (and the manual says it prioritizes on detecting the parallel port connection, and if found, then it disables the serial connection side).

So I'm not sure what else this could be used for. Has anyone made a kind of "phone network emulator" that we can plug in phone cables? I know we could just setup LAPlink parallel cables between two systems. But I'm still curious to see if this "Virtual COM port" concept works.

 

[voidstar78]

One reaosn I'm curious about this device is because the install disk has PPM.EXE, which appears to be some kind of TSR that can be loaded/unloaded in MS-DOS. But I can't find any documentation about this program, device driver, or whatever it is. It occupies about 14KB of RAM.

Is this just how similar device drivers worked with Win3.x? (i.e. they actually loaded as TSRs)

Or does this TSR somehow enable interfaces where MS-DOS could also access these "virtual COM ports"? The manual implies this device can work with Procomm Plus (MS-DOS) (because it has sections for both Procomm Plus and separate one for Procomm Plus for Windows). But not sure if that's while at a DOS prompt while Windows is running [ under WINDOWS\SYSTEM its drivers are PPM.VXD, PPM.386, PPM.DRV - the PPM.EXE TSR when loaded from straight MS-DOS doesn't seem to be aware of those driver files, so don't think they are related?? ]

So was hoping some kind of ex-Microcom expert is around who might be familiar with this program.

 

[voidstar78]

The only reference to PPM.EXE I find is in the included README.TXT after the installation.

I'm not familiar with NCSI/NASI - probing into that, it seems like extensions to Int 14h?? Or something MS-DOS Kermit might support (or possibly pcAnywhere), maybe for some "extreme remote desktop" kind of features (stuff that would appreciate high speed bandwidth than old school 9600 baud or slower).

So it seems this device would help on those older systems when modem-comm was still a thing. But these days there just isn't much we can do with these things (I haven't had a land-line for about a decade now). Is twisted pair RJ11 a thing? Could I direct connect one modem to another?

NOTE: This same README.TXT does reference Win95 (in terms of specifying a IRQ to use with this Parallel Port driver). So it's possible the VXD might work with Win95. I don't have any Win95 systems setup at the moment.

 

[krebizfan]

Twisted pair RJ-11 does exist. Slightly more expensive than the non-twisted counterpart.

Connecting two modems together requires a line simulator to produce the expected current of a phone line. https://www.mumris.eu/SP2.htm shows one concept. Check your modem manuals for how to not look for dial tone which won't exist.

 

[MauriceH]

"..

Has anyone made a kind of "phone network emulator"

Just find your self a small Home Vox ,like a one to connect/dial 4 or 6 phones.

I use one to connect very old computer, through modems,to the downstairs terminal.
2 old rotary dial phones, just having fun.

You could indeed use the mentioned battery solution for now, but the fun to really dial in, your missing.

To get into your modem look for; "Hayes modem AT strings and commands".
There to find how to setup your modem, directly open your modem without dial in, set up baud rate, etc.

 

[voidstar78]

Here's the only online notes I can find (on internal jumpers and then AT commands)

DESKPORTE FAST

Also not there is Microcom DeskPorte FAST and Microcom DeskPorte FAST+ (I think the "+" difference is only that it supports 33.6 instead of only 28.8).

I do have the printed User Guide, 200+ pages that covers more details on these commands. There is a Direct Mode mentioned related to internal SW2. There is also an "ATDU" command describes as an override to force direct mode dialing (haven't tried it yet, and not really sure what it means; don't see any elaboration in the manual).

One interesting thing on this modem, when in Command Mode, you can only type "AT". That is, most modems will echo back whatever you've typed. But this one, it is actively searching for "AT" first to indicate attention and specifying a command. After the "AT" then you can type whatever you want to complete whatever the intended command is. I just hadn't seen that before in other modems.
NOTE: apparently this is "smart" vs "dumb" mode, you can disable this Smart Mode using AT-h (pg208 in manual)


It also has an "autobaud" feature, so you can open the terminal in "whatever baud" and upon typing AT the modem attempts to automatically resolve the speed.


Other notes: AT\N1 sets operating mode (mode 1 being direct mode)

I have two of these, but still not fully understanding Direct Mode. Notes in the manual don't fully described it, but it mentions that Flow Control is disabled in direct mode.

 

[MauriceH]

..Not fully understanding Direct Mode..

Back in the day's as a company you could order a direct open line at your phone company.
That is to know just 2 or 4 wires that is f.i. connected to an other office somewhere.
Its not a dail in line, but open for you 24/7.

There is no power on those lines, Just 2 or 4 wires.
At the Phone company, those lines could be stacked up in multiple/Multiplex, amplified etc or other systems to further
transport signals to somewhere out in City or States/Countries what ever and at the other end finally ends up in again 2 or 4 wires.

Used to install those lines with modems, designed/route them also, that is implement them in the Phone company computer systems.
Those modems by then have an own open continuously connection 24/7 with the other side, like a modem attached to a computer.

You all maybe think a Phone company is about the dial phone, but its only part of their business.
Great deal is about so called fixed-lines between locations.

Think about all situations a system needs to be controlled from a long distance.
Even back in the day's when we all start paying digitally with your bank card an pin number,
all those little boxes had a modem fixed connection,so no dial in.

 

[jhodge]

Hey - I owned and used one of those in the 90s. The parallel port connection was necessary if you had an 8250, 16450, or a pre-"a" 16550 with a buffer that didn't work right to get reliable performance at 28.8kbps. It's been a while, but I *think* that the serial connection may have been OK under plain DOS on a sufficiently quick system, but if you were running OS/2, or Desqview, or Windows the parallel port connection was the way to go for reliability.

IIRC once the driver was loaded, any comm software could be used. I know I never used Procomm Plus because I primarily used OS/2 in those days and used HyperACCESS/5 from Hilgraeve with that modem for years.