Comments on: Building OnChange event to listen the parallel port

By: robert hacault

robert hacault — Tue, 12 Jan 2010 18:12:47 +0000

got it to work

By: robert hacault

robert hacault — Fri, 08 Jan 2010 18:23:01 +0000

I have my code working but I have a question on the pins

I am trying to receive some inputs from the port.

I know the 8 data pins are used for output
I can receive the input of the 5 status pins but for some reason I cant find a way to receive input data from the 4 control pins. I though they were I/O. if so , what am I doing wrong?

By: Pablo Romano

Pablo Romano — Mon, 14 Dec 2009 18:26:03 +0000

Hi Bennyben,
I guess you want to send a 0 to a particular pin, but when you write to the port you must send 1s or 0s to all the others too.

Reading and writing can be done through PortAccess.Input and PortAccess.Output. The latter receives the address and a decimal value that is converted to it’s binary form, where each bit correlates to a pin. Here is a link explaining what you can do with each pin.
http://www.beyondlogic.org/spp/parallel.htm#5

If you want to change the value of one pin first of all you need the value of the others, the ones that don’t change. If you are working with the bi-directional pins you can read the value, if you are using the write-only ones you must keep the value in your application.

Let’s suppose the value is 11011011 = 219 dec and you want to send a 0 to the 4th pin (bit 3), then you should make a mask that has a 0 in that position, 1s in all the others and make a bitwise and (&) with the current value. Here is an example:

int currentValue = 91; //01011011

int mask = 255 - (int)Math.Pow(2, 3); //11111111 - 1000 = 11110111

int newValue = currentValue & mask; //01110111 & 11011011 = 01010011

If you want to send a 1 to a pin you should make a mask with 1 in that pin, 0s in all the others and make a bitwise or (|) with the current value.

Please tell me if this helps or you need more assistance.

By: bennyben

bennyben — Mon, 14 Dec 2009 03:17:06 +0000

how to deactivate a certain pin?
i know that ‘PortAccess.Output(address, 0)’ is to deactivate all the pins.

By: Pablo Romano

Pablo Romano — Sun, 18 Oct 2009 15:55:36 +0000

Hi Miguel,
I haven’t tried the code with a usb to parallel, I think in the worst case only a change in the PORT_ADDRESS constant will be needed.

Try it and let me know

By: Miguel Hidalgo

Miguel Hidalgo — Sat, 17 Oct 2009 14:57:53 +0000

Excelent article, but I have a question: Does it works with a USB to parallel cable (1284)? I am looking to access the pins of the this port with the cable.

Thank you

By: Pablo Romano

Pablo Romano — Mon, 21 Sep 2009 14:31:57 +0000

Hi Niraj,
The code listens all the pins, it translates the binary number to it’s decimal form.
If you only need the 10th pin you can mask the others by doing “bool pinState = (readedNumber & (int)Math.Pow(2, 6)) != 0;” (http://www.ctv.es/pckits/tutorial.html#padr)

Please tell me if this helps or you need more assistance.

By: niraj

niraj — Mon, 21 Sep 2009 05:44:17 +0000

hello is it listen to lpt pin no 10????????? plz replay soon

By: wilman

wilman — Mon, 20 Apr 2009 17:30:15 +0000

Pablo,

I have already figured it out myself after trying but thanks a lot for typing it since it will be useful for others I think. The project worked great with this. Go ahead, really nice blog!

By: Pablo Romano

Pablo Romano — Fri, 17 Apr 2009 13:54:07 +0000

Hi Wilman,
Thanks, I’m glad you liked it!

Here is an example, if you have any doubts tell me.

Greetings from the other side of the Rio de la Plata,
Pablo

Example:

class DemoClass
{
public DemoClass()
{
PortListener.ParallelPortListener.Instance.OnPortChanged += OnPortChanged;
}

void OnPortChanged(int portValue)
{
//Do something with portValue
}
}