same interrupt, different addresses?

[david nugent]

In <9102042023.AA04935 at enuxha.eas.asu.edu> gomez at ENUXHA.EAS.ASU.EDU (Jose L. Gomez-Rubio) writes:

> I'm looking to add a COM3 & COM4 serial port to my 386 UNIX box.  Is it
> true that each COM port must have it's own interrupt or can they share
> an interrupt but reside at a different address?

That's dependant entirely upon the card.

The majority of 4 port cards I've seen do not support shared interrupts.
I wouldn't guarantee results unless the card's documentation specifically 
states that it does have this support.

The next problem you'll have is installing a driver which can support 
them, if the card is not explicitly supported by your OS. FAS (2.08 I 
gleefully noticed was just posted here :-)) should provide what you 
would need.


> Anyone know of a COM3&4 board that does not use INT 4 & 3?

Some have jumpers, which may be used to select different IRQ's - you
shouldn't have too much difficulty finding one.  I've found one of 
Everex's cards quite reliable.  However, with only 5 or lessIRQ's to 
choose from (6 if you want to give up your floppy drive), that doesn't 
leave much room for additional 8 bit devices.  On a Unix, you'd probably
be better off with either a dumb card which supports 4 or more ports
(such as the Digiboard or AST cards) or, even better, an "intelligent"
(processor driven with their own interrupt controller) adaptor, since
you loose little in CPU power in servicing the additional ports.

As with most things, you pay for what you get - these cards are more
expensive. I'd recommend either the Stallion range of boards (with 
which I've had great success over the last few years) or Digiboard 
COM/iX intelligent cards.  Since I've had little trouble with either 
and both are easily available here, I haven't tried nor can comment 
on other similar products.


Regards,

	david

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