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Where can I find quality 25-pin serial card...?

Posted on 1999-07-08
Medium Priority
Last Modified: 2012-08-14
Actually, I have a few questions, experts!
1.) Where can I purchase 25-pin serial port cards?
2.) Can you purchase serial cards for ISA as well as PCI?
I need to add a second serial port to a Micron ClientPro PC.
I would appreciate any advice on a model that will not cause
problems with Win95's PNP IRQ's.


Denmark W.
Question by:denmarkw
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Expert Comment

ID: 1158716
I have some OLD ISA 25-pin serial cards from 386/486 vintage.  I haven't seen anything newer since they are mostly built-in.  These old cards are usually hardwired to COM2/COM4 IRQ3, although a few have jumpers.  Suggest checking your local flea market, buy a 486SX and take the card.
LVL 13

Expert Comment

ID: 1158717
a company that makes an assortment of I/O products, including hi-speed serial/parallel is Data Technology Corporation ( I have used their products thru the years, good quality, and they even have tech support.


Expert Comment

by:Shawn Connelly
ID: 1158718
We have an absolute requirement for high-quality serial cards.

Without exception, the only product we trust is made by a company called Lava components.  This is a small Canadian manufacturer.  They manufacture a variety of peripheral cards (including serial).  I've been dealing with this highly respected company for over ten years now.  Zero defects out of nearly $50K dollars of product in ten years is pretty good by anyone's criteria.

You may find LAVA at:

See the following for references:

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LVL 11

Expert Comment

ID: 1158719
It sound like from your previous cable question you are going to be needing more than standard PC serial ports, which do not implement more than 9 connections, your best bet here is to get some designed to be used for data aquisition from laboratory and monitoring equipment which implement the full RS 232C protocol and include the current loop - & + transmit and recieves and are capable of providing the specced +25v & - 25v line drives for those long runs rather than the 12v or so that most PC ports get away with.

These guys appear to have what you will be needing but at a price....

A nose around in that section will offer you a lot of configurations to choose from.

Author Comment

ID: 1158720
Road warrior,

We need to use the cables to connect Async Wang terminals to
a Motorolla multiplexor for remote connectivity. We will use the extra 25pin Serial port for local connectivity.
I'm not sure about the pinouts for this application.
Where can I find the specs?

Expert Comment

by:Shawn Connelly
ID: 1158721
If you're going long distances, you should go RS422 rather than RS232.  Still, give LAVA a call (they manufacture a large variety of serial costs including RS422), I'm positive they can help you out at a reasonable cost.
LVL 11

Expert Comment

ID: 1158722
Any standard PC serial card with a brand name on it and a warranty with it is probably going to give you satisfactory performance for local connectivity, if you are connecting PC to PC a 7 wire "null modem" or "serial laplink" cable is probably sufficient, these can usually be picked up premade in lengths up to 25 feet in any computer shop with a reasonable range of cables. What are you connecting the PC's to?

Author Comment

ID: 1158723
The 25pin cables we need are for connecting Wang display
stations to a Motorolla Multiplexor.
What are the standards for RSC232 serial cables?
Is there a maximum run length?
For longer runs don't we need to use higher quality cables?
What does the AWG# indicate?

Denmark W.
LVL 11

Expert Comment

ID: 1158724
Okay, here is a real goodie, an online cable designer that should let you do the wiring for each run and piece of equipment correclty... 

(working at the moment but reportedly sporadic)

I am working from recieved wisdom at the moment, I have heard that rs232 standards specify cable runs shorter than 50 feet, attempting to find hard answers as to how and why longer cable runs work and what you need to do to ensure it.
LVL 11

Expert Comment

ID: 1158725
here is a quote from

""The standards for RS-232 and similar interfaces usually restrict RS-232 to 20kbps or less
                and line lengths of 15m (50 ft) or less. These restrictions are mostly throwbacks to the days
                when 20kbps was considered a very high line speed, and cables were thick, with high

                However, in practice, RS-232 is far more robust than the traditional specified limits of
                20kbps over a 15m line would imply. Most 56kbps DSUs are supplied with both V.35 and
                RS-232 ports because RS-232 is perfectly adequate at speeds up to 200kbps. You may
                remember the "zero slot LANs" that were popular a few years ago, using RS-232 ports on
                PCs running at 115kbps. At Sangoma we have successfully used RS-232 (albeit on short
                cables) at line speeds of over 1.6Mbps.

                Interestingly enough, most RS-232 ports on mainframes and midrange computers are
                capable of far higher speeds than their rated 19.2kbps. Usually these "low speed" ports will
                run error free at 56kbps and above.

                The 15m limitation for cable length can be stretched to about 30m for ordinary cable, if well
                screened and grounded, and about 100m if the cable is low capacitance as well. Our
                standard test cable at Sangoma is an interconnected run of round and flat cable, about 25M
                in length, with no screening at all. We run error free on this cabling collection at up to

end quote,

So it would appear that if you wire as per on low capacitance cable, then you will be getting what you need.


Road Warrior


Author Comment

ID: 1158726
We don't actually need high speed communications.
The multiplexor speeds are set at 9600bps for each connection.
But because the runs could be greater than 50ft., do we need
higher quality RSC232 cables? How are they graded or categorized?

Author Comment

ID: 1158727
What is the specs. on RS422?

Accepted Solution

satwa earned 300 total points
ID: 1158728
The Company is JDR Microdevices - tel.: 1-800-538-5000

They sell 2 cards with 25 pin serial ports.
card 1. - PCI SERIAL CARD - ask for 25 Pin one.

card 2 - ISA High-Speed Serial Card - ask for the 25 pin one

Card no. 1 is plug and play and will not interfere with anything provided that
you have the spare IRQ's and DMA for windows to set it up under plug and play.

Card no. 2 - you have to set the IRQ addresses yourself on this one.

Expert Comment

by:Shawn Connelly
ID: 1158729
Hello Denmark:

First of all, for your curiosity, RS stands for Recommended Standard.  The reason I'm pointing this out is that the specifications are just that, a recommended standard.  You may go beyond the max. specs. with success.  Having said that, here are the specifications for both RS232 and RS422.
BTW, see the following for more details:

Max. Distance:
RS232 - 50ft at 19.2kbps ; RS422 - 4000ft at 100kbps

Max data rate:
RS232 - 19.2kbps (although in practice, this is normally higher)
RS422 - 10Mbps at 50ft

Signaling (this makes the important difference!):
RS232 is unbalanced whereas RS422 is balanced.
Rather than re-invent the wheel, see the above web page for a definition of what this means.

Clearly, RS422 is the best method to use for long distance serial data communications.  Again, see LAVA they make the best RS422 devices in the industry for a surprisingly inexpensive price (under $100.00 CDN).


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