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Date:      Thu, 03 May 2001 12:22:26 -0600
From:      Brett Glass <brett@lariat.org>
To:        Terry Lambert <tlambert@primenet.com>
Cc:        tlambert@primenet.com (Terry Lambert), dchulhan@uwi.tt (Dale Chulhan - Home), chat@FreeBSD.ORG (chat@FreeBSD.ORG)
Subject:   Re: Modem Woes
Message-ID:  <4.3.2.7.2.20010503121741.045d38d0@localhost>
In-Reply-To: <200105031815.LAA29153@usr05.primenet.com>
References:  <4.3.2.7.2.20010503114324.0459d260@localhost>

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At 12:15 PM 5/3/2001, Terry Lambert wrote:

>Brett, these are multiport cards, which have interrupt coelescing
>logic on the multiport card, 

There isn't any fancy logic.... It's just a "wired OR," since
the UART chips have open collector IRQ outputs.

>PC motherboards can not share ISA interrupts, period, 

It is true that two separate ISA cards can't share IRQs. However,
many motherboard chipsets are now designed so that a UART on the 
motherboard can share an IRQ with an ISA card successfully. The 
motherboard chip makers have done this to forestall endless 
complaints from users.

>It is highly probable that we are talking about an IRQ conflict,
>given that he _already stated_ that he was plugging a modem in,
>_AND_ that Windows rec0ognized it as COM4 without being beat over
>the head with a 2x4 or having a new driver loaded.

Windows assigns "COMx" port numbers without regard to I/O port
address or IRQ number. While it says "COM4:", you may discover
that the board uses, say, IRQ 11 and I/O base address 300.

--Brett


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