C / C++ / MFC

9-Aug-04 19:44

HI,

How can i read n write uing parallel Port

can any body tell me. with sample plz
thanx

Regards.

Antti Keskinen9-Aug-04 21:22

9-Aug-04 21:22

There are numerous examples here on Code Project about the programming of serial and/or parellel port.

Here's one of them, showing you how to control LED's with parellel port. The article is written by Jaygiri. The article[^].

Read the article through, and you will understand more of how the parellel port works. For even more detailed information, see this article[^]. It's written for C#, but the technical reference at the start is essential.

-Antti Keskinen

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The definition of impossible is strictly dependant
on what we think is possible.

zahid_ash9-Aug-04 21:33

9-Aug-04 21:33

thay all show how to write data there ,

but i also read data from there send by device

tll me abut read
thanx

Regards.

Antti Keskinen10-Aug-04 0:08

10-Aug-04 0:08

First, point your browser to this location: http://www.logix4u.net/inpout32.htm

In there, download the Inpout32 binaries and sources. From this zipfile, extract the files inpout32.dll and inpout32.lib. Place these into your project directory.

Open up your project, and go to project settings. Link with "inpout32.lib" to gain access to two functions: Inp32 and Out32. You also need the definitions of the functions. They are as follows (add them to the start of the code module where you wish to use them, or create a header file):

extern short _stdcall Inp32(short PortAddress);
extern void _stdcall Out32(short PortAddress, short data);

Now, use the articles' instructions to determine the address of your computer's parellel port. Then use the Inp32 function to read from this address. The returned value is a short integer.

If you need to determine if a certain pin on the port is set to logic-1 (high), use the articles' instructions, or Google for 'binary operations'. The idea is to mask the returned value against a certain value. The result of the mask operation is either TRUE or FALSE, depending if the pin is set or not. There are so many examples of masking operations on the Net that I don't want to repeat them here.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

zahid_ash10-Aug-04 0:38

10-Aug-04 0:38

i got it ,,

i have little confusion now.

I m writing data on 0x378 address (data register)that goes to attached device

can i read data from it ,, mean to say that my
device can write data on data register pin that i want to register.

or it should write on status pins (10-15)

or only pins 2 to 9 can do both read and write

thax

Regards.

Antti Keskinen10-Aug-04 1:23

10-Aug-04 1:23

The pins of a MODERN (at least a Pentium III -grade computer/MB) parellel port are indifferent whether you are reading or writing. You can both read and write to the data port. This is called a bi-directional LPT port.

You can use the data port (0x378) to send data (write values from 0 to 255). The data is represented in binary format, with the D0 being the least significant bit and D7 the most significant.

You can also use the data port to receive data. If you use the D0-D7 pins, you can read from address 0x378. If you input the voltages to pins S3-S6, you use the address 0x379 to read the value. Remember that the input values on S3-S6 range from 0, 8 - 248, because pins S0-S2 are not physically there, although they exist for the computer. This means that if you read from the address 0x379, and only the S3 has voltage, the received integer is 8. If all S3-S6 have voltage, the value is 248. If none have voltage, the value is 0. Note that I am not 100% sure of these values. The easiest way is to physically put a suitable voltage there and see what the function returns.

Remember to use big enough resistors in your connections. The parellel port cannot handle big currents (output or input). It will break, and most likely also damage your motherboard. The maximum current running through a pin should be around 2-3 mA. This "should" be safe, however I cannot guarantee, and will not take responsibility. The best way is to use a TTL optocoupler that will physically disconnect the actual device from the parellel port. In this way, the data is transfered in TTL logic levels, but the currents will never go over the limits.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

zahid_ash10-Aug-04 1:59

10-Aug-04 1:59

thanx but a little problm again.

i m writing to data register a value assume 18.

in response my device should return me 33;

when i read it from data register ( the reply of device) it gives me the same value as i sended. 20.

wts the problm ,, my device is not properly updating(writng on ) data register .

is it .. or some other isssue

thanx

Regards.

Antti Keskinen10-Aug-04 2:41

10-Aug-04 2:41

This happens because both your application and the device are writing to the port at the same time.

The Inpout32 library, when you call Out32(), will set the port's pins to represent the value you specify. This means that the pins will stay powered even after the call is completed.

To initiate succesfull communication with your device through the same port, first use Out32(888, 0) to clear any previous outputs. Then write Out32(888, 18). Now make your device read the value in some way (press a button, for example). When done, write Out32(888, 0) again. Put your device to send data, and use Inp32 to read the value.

The problem itself is simple: both you and the device are issuing voltage to the port's pins. This means that if you write 00000001 and your device answers to this by putting 10000000, the port will end up with 10000001, unless you clear your own output first. So, the trick is to call Out32(888, 0) before reading the input.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

zahid_ash10-Aug-04 2:15

10-Aug-04 2:15

I also set the Control pin-5 to TRUE(1)
as for Bi Directional

but .....no

Regards.