> ><<I believe the problem is an overlap in IRQ addresses.  Doesn't COM3 use
> >the same address as COM1and Com4 as Com2 (normally)?>>
> >
> >Yes; the "standard" settings are
> > COM1: 0x3F8, IRQ4
> > COM2: 0x2F8, IRQ3
> > COM3: 0x3E8, IRQ4
> > COM4: 0x2E8, IRQ3
> >
> >Since the PC/AT architecture uses edge-triggered interrupt lines, it is
> >not possible to share an IRQ line between two devices.
> >
> >However, it is at least as likely that he is having a problem with his
> >I/O address; for unknown reasons, IBM used an I/O address range that
> >includes 0x2E8 when they designed the 8514/A video adapter. Since there
> >are a lot of video adapters that support this interface, including such
> >popular items as almost all ATI adapters and all current S3 chips, there
> >are a ton of video adapters out there that won't work with a COM4 device,
> >even if the user selects an unused IRQ line. Yuk.
> >
> >Steve Dirickson         WestWin Consulting
> >(360) 598-6111  [log in to unmask]
> I had the same problem on my PC when I configured my modem on COM4. I called
> Microsoft Tech support and diagnosed that I had a case of "sliding IRQ"!  What
> the  net of all this is:  You cannot have your modem configured on COM4 if you
> do not have a physical COM3 device configured - do you have a COM3 device?  If
> not try setting your modem to COM3 and see if that works.
>
> Dennis
>
 
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