preconfigured assigments

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Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

Hi
I am reading a course about A+. in One slide which has title of
"Interrupt Request Number (IRQ)" it is mention this

<quote>
COM and LPT are preconfigured assignments of system resources that
device can use
</quote>

Could you please tell me what does "preconfigured assigments" mean
here?? and why for COM and LPT??

thanks a lot

 

[Guest]

Archived from groups: alt.comp.hardware.pc-homebuilt (More info?)

"esara" <esara123@hotmail.com> wrote in message
news:fd7d27e7.0404301135.1aaa2e90@posting.google.com...
> Hi
> I am reading a course about A+. in One slide which has title of
> "Interrupt Request Number (IRQ)" it is mention this
>
> <quote>
> COM and LPT are preconfigured assignments of system resources that
> device can use
> </quote>
>
> Could you please tell me what does "preconfigured assigments" mean
> here?? and why for COM and LPT??
>
> thanks a lot

All communications between cpu and peripherals must have an address and an
IRQ. The IRQ is to sync communication between cpu and peripheral (so that
multiple peripherals don't all try to talk at once), the address is so that
the right peripheral will establish communication with the CPU. Certain
system resources are set aside for legacy ports, called "COM" and "LPT".
For example, each "COM" port has a default address and IRQ for a physical
serial port. The physical serial port that relates to the "COM" port can be
built into the motherboard or on an expansion card or even OUTSIDE the
computer. External modems often have a serial port, which can be assigned
to a particular "COM" port. In that case, it is often necessary to enter
the system's BIOS menus to DISABLE the "onboard COM" port. Otherwise, you
will have two chips responding to the same IRQ, with unpleasant results.
-Dave