HOW TO PROGRAM THE PARALLEL PORT ON A COMPUTER USING C/C++

New versions of windows operating system does not support direct access to I/O ports.

In order to communicate with the parallel port of your computer in windows operating system you will need a driver called inpout32.dll which you can dowload from here http://logix4u.net/parallel-port/inpout32_source_and_bins.zip

Extract the zip file , open the binaries directory , copy the inpout32.dll and add it to you projects directory.
you can also save it at "%systemroot%\system32\drivers"

The address of the parallel data port is 
0x378-0x37F for LPT1
0X278-0X27F for LPT2

Parallel port has 8 data input

fig.1

DATA PORT PIN NO.	SIGNAL NAME	BYTE TO ACTIVATE PIN
2	D0	0x01
3	D1	0x02
4	D2	0x04
5	D3	0x08
6	D4	0x10
7	D5	0x20
8	D6	0x40
9	D7	0x80
18-25	Ground(GND)

All the data port are latching which means it keeps it state once it is activated.

To send one byte to the parallel port  
 send 0xFF to 0x378

1 bit will be on each data port which means all the data port will have 5V across them

To send 1 bit to Data port 

If you send 0x01 to data port 0x378 will send binary 00000001(5V) to pin 1
and so on as shown on the table.

Now to start create a new cpp file  and note the inpout32.dll should be in the same folder or you can place in this directory %systemroot%\system32\drivers.

This is how your code should start

	#include <iostream>
	#include <windows.h>
	using namespace std;
	typedef short _stdcall (*inpfuncPtr)(short portaddr);
	typedef void _stdcall (*oupfuncPtr)(short portaddr, short datum);
	int main()
	{
	HINSTANCE hLib;
	inpfuncPtr in;
	oupfuncPtr out;
	hLib = LoadLibrary("inpout32.dll"); //load the inpout32.dll
	if (hLib == NULL) {
	cout<<"LoadLibrary Failed.\n";
	cin.get();
	return -1;
	}
	in = (inpfuncPtr) GetProcAddress(hLib, "Inp32"); //define in function
	if (in == NULL) {
	cout<<"GetProcAddress for Inp32 Failed.\n";
	cin.get();
	return -1;
	}
	out = (oupfuncPtr) GetProcAddress(hLib, "Out32"); //define out function
	if (out == NULL) {
	cout<<"GetProcAddress for Oup32 Failed.\n";
	cin.get();
	return -1;
	/* place your codes here
	use in(address) to read data from parallel port
	use out(address,data) to send data from the parallel port
	*/
	}

view raw main.c hosted with ❤ by GitHub

To send 1 bit to data port pin 1( D0 ) out(0x378, 0x01) and the rest can be found on the table 

Here is a simple example to demonstrate how to switch the data port of the paraport on and off .

setup a circuit as shown below

fig.2

And the source code is here:

	#include <iostream>
	#include <windows.h>
	using namespace std;
	typedef short _stdcall (*inpfuncPtr)(short portaddr);
	typedef void _stdcall (*oupfuncPtr)(short portaddr, short datum);
	int main()
	{
	HINSTANCE hLib;
	inpfuncPtr in;
	oupfuncPtr out;
	hLib = LoadLibrary("inpout32.dll");
	if (hLib == NULL) {
	cout<<"LoadLibrary Failed.\n";
	cin.get();
	return -1;
	}
	in = (inpfuncPtr) GetProcAddress(hLib, "Inp32");
	if (in == NULL) {
	cout<<"GetProcAddress for Inp32 Failed.\n";
	cin.get();
	return -1;
	}
	out = (oupfuncPtr) GetProcAddress(hLib, "Out32");
	if (out == NULL) {
	cout<<"GetProcAddress for Oup32 Failed.\n";
	cin.get();
	return -1;
	}
	int x;
	do
	{
	cout<<"\n select(0 to quit) \n";
	cout<<"1. data port ON \n";
	cout<<"2. data port OFF\n";
	cin>>x;
	if (x==1)
	{
	out(0x378,0xFF); //turn all data port high
	cout<<"port is ON\n";
	}
	else if(x==2)
	{
	out(0x378,0); //send 0 to data port pin
	cout<<"port is OFF\n";
	}
	}
	while (x != 0);
	return 0;
	}

view raw main.c hosted with ❤ by GitHub

Output display below

fig. 3

With this you can control many appliance and device with the help of a relay.
 The next blog is about How to use the Parallel Port to control a 240 V light bulb