8-bits as terminals (Was: Serial Multiplexor)

From: Sellam Ismail <dastar_at_ncal.verio.com>
Date: Mon Jun 14 18:45:27 1999

On Mon, 14 Jun 1999, Arfon Gryffydd wrote:

> >Probably to buy a cheap multiport serial card. Cyclades has some nice
> >unintelligent cards, as well as some nice (but quite spendy) intelligent
> >cards and terminal servers.
>
> You know of one for $25.00? That doesn't require and IRQ for every port?

I don't know about $25, but I do know of one that sells for around $299
that is 8-ports, uses 1 IRQ (from 3-15) and is a pretty damn nice board to
work with. It been tested in several OS's, including DOS, WIN95, WINNT,
and several flavors of Unix, and just maybe Linux (though I'm not sure).

You can chain up to 4 of these cards together for a total of 32 ports on
one interrupt. The board can be configured for base addresses from 200h
through 360h. The board has a 16550 for each port. To a communications
program, it looks just like a normal serial port so its easy to hack and
write drivers for. For instance, I can get it to work with ProcommPlus
with little effort. It helps that ProcommPlus is such a fine program, but
it has a setup whereby you can assign the base address and interrupt for
each COM port. Each port on the board is the base address + (8 * (p - 1))
where p = the port number. So if the board is jumpered at 280h, you'd
have port 1 at 280, port 2 at 288, port 3 at 290, 298, 2a0, 2a8... The
interrupt is the same for each port. So I just program the base addresses
for each COM port in ProcommPlus (up to 8) and the same interrupt and I
can now access every serial port on the card. Nifty!

$299 is still pretty steep for a fun-project, but I can't think of
anything else, besides getting lucky and finding one at a swap meet or
whatnot. I once scored a 16-port Digiboard and external connector box for
like $5 at a local computer recycler. Almost new, in the box. I'm
planning to either use it or the above mentioned multi-port card for when
I finally get my classic computer host online.

You can find the multi-port card for sale at the following web site. I
don't think these guys are the only distributor, and in fact you should
shop around because this web site is a software house that develops the
C serial port communications library I use in my projects, and so I'm sure
they are charging a premium.

http://www.wcscnet.com/Hardware.htm

The 4th card in the list is what I use. It comes with an external pod
that has the actual DB-25 connectors on it and connects to the card via a
big fat cable. Careful with this one if by chance you end up ordering
one...I've had two bad cables from the factory from the 15 or so that I've
ordered. Some of the lines were broken inside the cable, so that some
lines were missing on some ports. It doesn't affect all the ports, and it
doesn't the ports in the same way if more than one line is broken.

There's also a 4-port card listed there, and there are cards that do
RS-422.

The card is manufactured by Decision Computer Group. What do you know?
Here's their website:

http://www.decision.com.tw/

Sellam Alternate e-mail: dastar_at_siconic.com
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Received on Mon Jun 14 1999 - 18:45:27 BST

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