which com ports to assign for modems ?

Archived from groups: microsoft.public.win95.general.discussion (More info?)

The PC has a com1 (external, unused) port. An internal modem uses com3. If
I install a second internal modem, which com port does it want to be
assigned to ? This is all on win95.

Archived from groups: microsoft.public.win95.general.discussion (More info?)

"Bill" <billnh2001nospam@yahoo.com> wrote in message
news:eaC5LrDJFHA.3788@tk2msftngp13.phx.gbl...
> The PC has a com1 (external, unused) port. An internal modem uses com3.
If
> I install a second internal modem, which com port does it want to be
> assigned to ? This is all on win95.
>
>

2 or 4 to prevent an IRQ conflict with the existing modem.

Archived from groups: microsoft.public.win95.general.discussion (More info?)

"Tim Slattery" <Slattery_T@bls.gov> wrote in message
news:h90u21d2arrku3tv434al8u1jb04mr5j1o@4ax.com...
> "Kay Archer" <kayhyphenarcher@mail.com> wrote:
>
>>
>>"Bill" <billnh2001nospam@yahoo.com> wrote in message
>>news:eaC5LrDJFHA.3788@tk2msftngp13.phx.gbl...
>>> The PC has a com1 (external, unused) port. An internal modem uses com3.
>>If
>>> I install a second internal modem, which com port does it want to be
>>> assigned to ? This is all on win95.
>
>>2 or 4 to prevent an IRQ conflict with the existing modem.
>
> Right. One of the problems with COM ports is that COM1 and COM3 use
> the same IRQ line (I forget which one it is), and COM2 and COM4 share
> another. So, although there are four COM ports designed, you really
> can only have two active at once.
>
> Another reason to be glad the world has moved to USB.
>
> --
> Tim Slattery
> MS MVP(DTS)
> Slattery_T@bls.gov

IIRC I used to disable serial port 2 in the bios , then the internal modem
would take over the function of com 2 and use IRQ 3 (com3 is IRQ 4)

Archived from groups: microsoft.public.win95.general.discussion (More info?)

"John John" <audetweld@nbnet.nb.ca> wrote in message
news:eZedhyLJFHA.572@tk2msftngp13.phx.gbl...
> Tim Slattery wrote:
>
> > Right. One of the problems with COM ports is that COM1 and COM3 use
> > the same IRQ line (I forget which one it is), and COM2 and COM4 share
> > another. So, although there are four COM ports designed, you really
> > can only have two active at once.
> >
> > Another reason to be glad the world has moved to USB.
>
> I could never figure out why, with all the leaps and bounds in computer
> technology, that IRQ's were for the longest time limited to 15?

16, zero through fifteen (g).


To
> boot, as you mention the first group of 5 or 7 IRQ's are used by
> different devices and some are cascades or redirect to other IRQ's! Not
> to mention sound cards from hell that can be picky when it comes to IRQ.
> Windows IRQ sharing took care of some of the problems but still I
> can't understand why the motherboard manufacturers didn't engineer 50
> IRQ's years ago! I went here and took a little 2 minute test, but I
> won't tell you my score, too embarrassing! http://studynotes.net/QIRQ.htm
>
> John
>
> PS my score was 21%! It's been a long time since I fiddled with IRQ's.
>

Archived from groups: microsoft.public.win95.general.discussion (More info?)

"Kay Archer" <kayhyphenarcher@mail.com> wrote:

>16, zero through fifteen (g).

But I believe number 2 was used to connect the first IRQ bank to the
second, wasn't it? So you could only actually use 15.

--
Tim Slattery
MS MVP(DTS)
Slattery_T@bls.gov

Archived from groups: microsoft.public.win95.general.discussion (More info?)

John John <audetweld@nbnet.nb.ca> wrote:

>Tim Slattery wrote:
>
>> But I believe number 2 was used to connect the first IRQ bank to the
>> second, wasn't it?
>
>Cascade to IRQ 9. How many IRQ's in todays computers, 26 or 29?

I have no clue. With all kinds of peripherals using USB you very
rarely have to worry about IRQs anymore.

--
Tim Slattery
MS MVP(DTS)
Slattery_T@bls.gov

Archived from groups: microsoft.public.win95.general.discussion (More info?)

"Tim Slattery" <Slattery_T@bls.gov> wrote in message
newsek03195sg9ugpo2rotm5iqdj5g15t3ipo@4ax.com...
> "Kay Archer" <kayhyphenarcher@mail.com> wrote:
>
> >16, zero through fifteen (g).
>
> But I believe number 2 was used to connect the first IRQ bank to the
> second, wasn't it? So you could only actually use 15.
>
Use? I'd say less than 15. Did you ever put anything on IRQ0? Depends on
how you define useable... (Still with a (g)).

















Signature:
Never attribute to malice anything that can be ascribed to simple stupidity.

Archived from groups: microsoft.public.win95.general.discussion (More info?)

It's used by the System Timer.

John

Kay Archer wrote:

> "Tim Slattery" <Slattery_T@bls.gov> wrote in message
> newsek03195sg9ugpo2rotm5iqdj5g15t3ipo@4ax.com...
>
>>"Kay Archer" <kayhyphenarcher@mail.com> wrote:
>>
>>
>>>16, zero through fifteen (g).
>>
>>But I believe number 2 was used to connect the first IRQ bank to the
>>second, wasn't it? So you could only actually use 15.
>>
>
> Use? I'd say less than 15. Did you ever put anything on IRQ0? Depends on
> how you define useable... (Still with a (g)).
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> Signature:
> Never attribute to malice anything that can be ascribed to simple stupidity.
>
>

Archived from groups: microsoft.public.win95.general.discussion (More info?)

It depends on the hardware more than the operating system. The original PC
ISA bus was constructed in such a way that it was not possible for more than
one device to properly share the IRQ. USB uses one IRQ for the controller,
and decodes device IDs for itself. The technique that USB uses is not
actually new - it's the same technique that had been used for many years if
many (eg, 16) serial ports had to be used with an ISA bus. The serial port
interface card used one interrupt for its interface to ISA, but decoded port
numbers for itself to provide individual access to each serial port through
a single interrupt number. PCI works similarly, providing it's own internal
interrupt structure to enable multiple devices to function through each CPU
interrupt.
--
Jeff Richards
MS MVP (Windows - Shell/User)
"John John" <audetweld@nbnet.nb.ca> wrote in message
newsGpAJcjJFHA.2136@TK2MSFTNGP14.phx.gbl...
> In that case, as Tim said, thank God for USB. But that's of little use to
> Windows 95 users so someone has to know the abc's (or 123's) of IRQ's.

Archived from groups: microsoft.public.win95.general.discussion (More info?)

According to the test on page http://studynotes.net/QIRQ.htm you scored
57%. You did indeed have 14 and 15 reversed. Had you given those
answers your score would have been 71%, but as you already know the
Academy cannot allow students to change their answers after tests have
been turned in so we must inscribe a test score of 57% in your student
records. At this time we would like to inform you that Mr. John John
was caught last night trying to hack the Academy student records to
falsify his test score. Mr. John has been suspended.

Sincerely;

Dewey Dweeb
Academy Dean

Kay Archer wrote:

> "John John" <audetweld@nbnet.nb.ca> wrote in message
> news:%23i5p2cjJFHA.2136@TK2MSFTNGP14.phx.gbl...
>
>>It's used by the System Timer.
>>
>>John
>>
>
> From memory:
>
> 0 system timer (I might have said clock without John's help)
> 1 keyboard
> 2 redirect to IRQ9
> 3 com 2/4
> 4 com 1/3
> 5 typical uses: NIC or soundcard (some of which could not be changed,
> argh!)
> 6
> 7 lpt1
> 8
> 9 redirect from IRQ2
> 10 p/s 2 mouse port
> 11
> 12
> 13
> 14 scsi controllers (typical)
> 15 hdd controllers
>
>
>
> I used to be able to do this on a chalkboard while giving an hourlong
> lecture on the subject...
> I may have 14 and 15 reversed.
> 10 out of 16 only gives me about 60%.
>
>

Archived from groups: microsoft.public.win95.general.discussion (More info?)

When IBM added the second 8259 in the AT they had to cope with the fact that
the CPU only supported one hardware interrupt line, so they had to make the
two 8259s look like one large one. They did this by connecting the
interrupt output of the second device to IRQ2 of the first device, so the
interrupt line of the CPU is only driven by the first 8259. So ANY interrupt
from the second device looks like interrupt 2, and the routine at this
interrupt has to decode the status of the second 8259 to find what the
interrupt really was.

Of course, this would have made IRQ2 unavailable, so this interrupt line was
wired into IRQ9 (interrupt line 1 of device 2). The service routine at
interrupt 9 calls interrupt 2 (like all interrupts through the second device
do). So IRQ2 is still available (via the deciding at the service routine)
but IRQ9 is not available because that interrupt line isn't connected to
anything.

However, this arrangement, designed for PC add-on devices that might have
used IRQ2, seems to have been dropped somewhere along the way, and interrupt
line 9 is now wired through to IRQ9, and IRQ2 is marked unavailable. It
doesn't actually matter which way around things are, as long as the
interrupt service routines understand the physical arrangement of the
machine, and plug-in cards don't attempt to use the unavailable interrupt.

It is correct that ISA interrupts cannot be shared, but this is due to the
ISA bus architecture. Sharing interrupts depends on two things - the signal
levels and protocols that allow more than one device to drive the interrupt
line, and a mechanism for the software to work out which device actually
generated the interrupt. Although the ACPI interrupt is listed as ISA, it's
actually raised by the motherboard chipset, so presumably there are features
in the chipset design that allow it to be shared.
--
Jeff Richards
MS MVP (Windows - Shell/User)
"John John" <audetweld@nbnet.nb.ca> wrote in message
newst4GlTwJFHA.3916@TK2MSFTNGP14.phx.gbl...
> Thanks Jeff, you have explained something that I just couldn't and didn't
> bother to figure out for many years, IRQ sharing. If I may indulge and
> pick at your brains a bit more with this device IRQ sharing, this is the
> IRQ list for my Windows 2000 home pc. IRQ2 cascades to IRQ9 and
> ...hmmm... how can all these devices on IRQ9 work without conflicting with
> each other or rather, how can they all work simultaneously?
>
> ******************** IRQ SUMMARY ********************
> IRQ Usage Summary:
> (ISA) 0 System timer
> (ISA) 4 Communications Port (COM1)
> (ISA) 6 Standard floppy disk controller
> (ISA) 8 System CMOS/real time clock
> (ISA) 9 Microsoft ACPI-Compliant System
> (PCI) 9 NVIDIA GeForce2 GTS/GeForce2 Pro
> (PCI) 9 Win2003 Promise Ultra133 TX2 (tm) IDE Controller
> (PCI) 9 Creative SB Live! Basic (WDM)
> (PCI) 9 U.S. Robotics 56KVoice PCI
> (PCI) 9 Intel(R) 82801 BAIBAM USB Universal Host Controller -2442
> (PCI) 9 Intel(R) 82801 BAIBAM USB Universal Host Controller -2444
> (PCI) 10 Intel(R) 82801 BAIBAM 5MBus Controller -2443
> (ISA) 12 Microsoft PS/2 Port Mouse (IntelliPoint)
> (ISA) 13 Numeric data processor
> (ISA) 14 Primary IDE Channel
> (ISA) 15 Secondary IDE Channel
>
> I'm sure glad IRQ sharing exists because I would have had a bitch of a
> time trying to get all that stuff to work the old fashion way!