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Modem and Parallel Port Problem

By Shanghai Sam ·
Here's one for you. I frequently connect my laptop and desktop computers together via a Direct Parallel cable. One day after transfering some files I tried to go online. When dial-up networking tried to make the connection with my ISP it sounded a long tone and eventually disconnected. I uninstalled the drivers and reinstalled a newer driver thinking it was a driver problem.

Today, Is when I noticed the connection between the Modem problem and my parallel direct cable connection. I physically hooked my two computers together and before making the actual DCC connection between the two computers I tried to go online to get my email. Guess what, the problem mentioned earlier returned (long tone and disconnected). The only thing I could figure was that the direct cable connection was messing with the modem somehow so I removed the Direct Parallel cable from the Parallel port (without shutting down first) and attempted to connect again. Guess what? The modem connected with noproblem.

My question is why can't I connect with my ISP if I'm connected to my laptop (no actual connection was ever established between the two, just a cable running from the laptop to the desktop)? When my printer is connected there is no problem. What connection does the Modem and LPT 1 have?

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Modem and Parallel Port Problem

by TheChas In reply to Modem and Parallel Port P ...

Sounds like an IRQ conflict.
In device manager, click on my computer, and click on properties.
Check the IRQ and DMA lists to see if LPT and modem/comm port are sharing the same IRQ.

If so, see if you can change the LPT IRQ in setup.
You may also be able to change the comm port that the modem uses.

Also, if you don't use the serial ports, disable them to free up IRQs.

If these don't correct the conflict, you need to disable IRQ steering so that Windows will assign IRQ's differently.

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Modem and Parallel Port Problem

by Shanghai Sam In reply to Modem and Parallel Port P ...

The modem and lpt 1 really have no irq or com's
they can share or cross on newer systems! (the pnp bios won't allow it)

There were some modem's made when win95 came out That used drivers to load modem's into printer irq's these are usually ISAbus cards not pnp types. (Could apply to either system to)

however if you don't have one of these ISA card's by connecting the two computers with a parrallel cable you made a connection "like a null modem cable" but for the printer port.
there are a few thing's you can try. Like trying each type of printer mode, and changing printer port address (if your bios will allow it, not all will) try each computer with this.

I hope this will help

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Modem and Parallel Port Problem

by fenaikh In reply to Modem and Parallel Port P ...

It happend to me too.
Both Dial-Up Networking and Direct Cable Connection use the same network interface (Pppmac.vxd). You cannot have more than one instance of Pppmac.vxd running at one time.

Pls read more in this MS article

Good luck


Cannot Use Both Dial-Up Networking and Direct Cable Connection (Q14020;EN-US;Q140208

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Modem and Parallel Port Problem

by Addam Moody In reply to Modem and Parallel Port P ...

That VXD file is a more indepth explanation of the reasoning that I see behind it.

Both DCC and DUN use the 'dial-up adaptor'.
If the dialup adaptor is already in use, other programs can still attempt to use it, but it causes wierd problems - such as this one.

You'll probably find that if you try to DCC while you're also online, it either wont connect, or it will, and then the modem will drop out.

Many hours of messing about taught me this one

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