non plug and play device on com port?

  • Thread starter Thread starter David K
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David K

Question.

Charles Brooks' A+ cert book says the following in chapter 8:

"To install a non PnP device on a specific COM port (that is, COM2),
you must first disable that port in the system's CMOS settings in
order to avoid a device conflict. If not, the system might try to
allocate that resource to some other device because it has no way of
knwing that the non PnP device requires it."

If the BIOS won't know to automatically allocate resources to a device
unless it's PnP, how does the device ever get recognized? I don't
understand why disabling a comport is gonna help you get the system to
allocate resources to a non-PnP device. And are we talking about the
BIOS or the OS?

Is he implying that I should disable the port in the CMOS, plug in the
device, install the Windows drivers, then re-enable the port in CMOS?
If so, why would that help?

David
 
Question.

Charles Brooks' A+ cert book says the following in chapter 8:

"To install a non PnP device on a specific COM port (that is, COM2),
you must first disable that port in the system's CMOS settings in
order to avoid a device conflict. If not, the system might try to
allocate that resource to some other device because it has no way of
knwing that the non PnP device requires it."

If the BIOS won't know to automatically allocate resources to a device
unless it's PnP, how does the device ever get recognized? I don't
understand why disabling a comport is gonna help you get the system to
allocate resources to a non-PnP device. And are we talking about the
BIOS or the OS?
Click to expand...

Certain devices have traditional resources associated with it. Since
you're using COM ports, I'll use a modem example so we're on the same
page. On a typical motherboard, COM 1 and COM2 are associated with
the onboard serial ports, and with specific port addresses and IRQs.
You can change this, but usually these built-in ports aren't PNP, you
have to change the port settings with these connectors manually in the
CMOS.

Not a big deal with a PNP modem, since the PNP OS would simply notice
the potential conflict and keep trying its list of resource options
until it hits a combination that doesn't conflict.

The problem with a non-PNP modem is that since the resources it needs
are set in hardware (typically by dip switches or jumpers), the OS
can't just move the modem to different resources. It has to be THOSE
resources BUT those resources are already in use and have an owner --
The onboard serial ports. So, you get a conflict, which can result in
the system not booting, the system hanging when you try to use one of
them, or simply that neither device is available for use.

You have to choose which one you want to keep active since you can't
share resources unless the devices involved are able to do this. Not
many PC devices are capable of this, and those that are, don't always
do so successfully. This is why it's customary to disable a COM port
in the CMOS.

Is he implying that I should disable the port in the CMOS, plug in the
device, install the Windows drivers, then re-enable the port in CMOS?
If so, why would that help?
Click to expand...

No. Keep the port dead, or if the motherboard allows it, manually
remap the port so that you don't have any conflicts. Since the
non-PNP modem is an immoveable object, you can avoid the conflict by
removing one conflict source (the serial port) or reroute it (if
possible) so that it steers clear of the modem's resources.

Not too difficult, just imagine two stubborn kids in a playground who
don't get along. Your options for peace are remove both kids, remove
one kid, or try to keep kid A away from kid B. Having them shake
hands and be friends isn't always an option.
 
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