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Interfacing the LPT-port using C++ under WinNT

Posted on 2003-03-21
Medium Priority
Last Modified: 2008-01-16
I have made a digital circuit which I want to test using the parallel port (instead of a microcontroller). I thought this was very simple, bus I discovered "_outp" does not work under WinNT. Then I found some alternatives:
- use a VxD (???)
- use a device driver (where do I get such a driver and how to use it?)
- use CreateFile("LPT1", .....) en WriteFile() (how?)
What is the best way to send some bits to the 8 datapins on the LPT-port in Visual C++ (Win32 Console App)?
I am just a beginner in C-programming, so keep it easy ;-)

Hope you can help me.
Question by:Svens
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Expert Comment

ID: 8180508
I think CreateFile is the best, because it works from Win95 till WinXP and you don't need extra drivers (which is always a problem if you give the programm out of your hands).
Also with Createfile you can just use another device (eg. serial port or even TCP) with very little codechanges but i guess that's irrelevant for you :).


Expert Comment

ID: 8180595
It is not possible in NT (and XP,2000) to access hardware directly on the user level. You can write a device driver to access the hardware, but for the parallel port others did allready do the job.

Have a look at

You will also find a link to freeware drivers to access the parallel port directly ...


Accepted Solution

ivec earned 600 total points
ID: 8181375
You need a 3rd-party driver on WinNT.
For parallel port access, the free DriverLINX port I/O driver is very easy to install and use.
You can find it at: 95/NT Port I/O Driver

I used it for several projects, under NT/Win2000/XP/etc, without encountering any problem.

You just need to use a provided function call instead of directly reading/writing to an address.

Expert Comment

ID: 8183018
Yes, that's what I forgot to say: Using the driver is easier than struggling with the functions yourself.
Probably the driver is only a wrapper that translates an easy to use interface to the windows functions. Alone the fact that such drivers exist proofs, that it's not so much fun doing it yourself. Nevertheless you learn a lot and have the highest level of control, if you use CreateFile ;-).
If you don't need full control (asynchronous acess, change standard timings/timeouts our some other crazy stuff) using a driver is the quickest way to implement something.

That's really a nice link! :)


Author Comment

ID: 8244596
This is really the link I needed: It was very simple to me to install and use the software.


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