Hardware / How to Linux / IO

Parallel port control in Linux

by linuxgeek · Published October 10, 2014 · Updated June 18, 2015

The program pport is a simple yet handy program and its documented counterpart for accessing the output pins of multiple ports. Using this bundle, one can successfully control any household appliance or electronic device with minimal hassle and practically no changes. pport will alter the state (toggle or set) of the data pins specified by the user, of the parallel port or other supported ports using flippersto toggle or set, modifiers to alter the methods and provides information all availible from the contextual –help or -h options directly from the command line.Conceived to change between the low or high state of the data pins of the parallel port, development extended its use to other common PC ports:The i386 parallel port is a 25 pin D-shaped female connector in the back of the computer, conventionally used to connect a printer. Not all 25 pins are always needed. Thus it can alter the state of eight of those pins called data pins: 2, 3 4, 5, 6, 7 and 8. The rest are simple grounding pins as seen in the illustration below. Here is a scheme of the parallel port:

The data pins are D0 through D7. Pins 17 through 25 are the grounding pins.

The program also has support for the serial rs232 port. Although the IO is different from that of the parallel port, the serial connector rs232 can prove useful in many situations since it offers a serious amount of power (a voltage of +-12V or in some cases +-5V and short circuit current flow of 7-10mA) depending on the circuit types used in the PC circuitry. This is all at the cost of signal lines. The parallel port has eight data pins as we have seen above whereas the serial port has only three: TD(Transmit Data), DTS(Data Terminal Ready), RTS(Request to Send). However, only the last two are usable since TD is logic true(-12V) when no data is sent:

Based on the equivalence of both parallel port versions, pport accepts both standards transparently, either 9 pin or 25 pin serial rs232 connector.

Options

-p, –port <serial>: With this option one can select an alternative port.
-s, –set <pin1,pin2…|all|none|even|odd|random|dtr,rts>: Causes pport to set one, some, or all pins to high. Or to set all low with “none”. dtr and rts are available only in combination with the serial port. One can also use all and none with the serial port option in order to set both RTS and DTR lines to high respectively low.
-t, –toggle <pin1,pin2…|all|even|odd|random>: Causes pport to toggle the state of the specified pins.
-w, –wait <Nd|Nh|Nm|Ns>: Where n is a number, causes pport to wait a specific time before altering the state of the specified pins, where n is a number, and d stands for days, h for hours, m for minutes and s for seconds.
-r, –restore: Causes pport to restore the previous state of the pins stored in the data file.
–status: Makes pport give a status report on the parallel port.
–debug: Will turn on debugging for the following command.
–raw: Will send raw data through the parallel port.

Examples

Here are a few examples for using this program:

pport -s all -w 10m: Will set all the pins to high after a 10 minutes delay.
pport -s random -w 5s: Will set some random pins to high after a 5 seconds delay.
pport -r: Will restore the previous pin states. This can be useful if you want to include pport in your startup scripts so it can restore your device status on system startup.
pport -t 2,4,7 -w 10s: Will toggle pins 2, 4 and 7 into their complementary state after 10 seconds.
pport -p serial -s rts: Will set the rts line of the rs232 port to the high state.
pport -p serial -s rts,dtr: Will set both lines of the rs232 port to the high state.
pport -p serial -s none: Will set both lines of the rs232 port to the low state.
pport –raw “Hello world”: Will send data through the parallel port.

Notes

1. The pport utility, must be able to access the ports in the first place. Failure to do so will result in an error. Thus pport must have superuser priviledges at runtime.

Parallel Port Accessing using C Code

Below are listed two options for controlling the parallel port under Linux. The first option writes directly to the parallel port memory address. It’s simple and works well, but because of the low level access, you’ll need to have root privileges. The second option, uses the ppdev module for user-space access, that means you don’t need root privileges.

Compile either source file using the following command line.

> gcc cableTest.c -o cableTest

1	> gcc cableTest.c -o cableTest

#include <stdio.h>
#include <inttypes.h>
#include <sys/io.h>
#include <signal.h>

#define BASE 0x378

int running = 1;

void signalHandler(int sig)
{
   running = 0;
}

int main(void)
{
   printf("Parallel Port Interface Test (Base: 0x%x)n", BASE);

   signal(SIGINT, signalHandler);

   // Set permission bits of 4 ports starting from BASE
   int result = ioperm(BASE, 4, 1);

   // If setting permission failed, return
   if (result != 0)
   {
      printf("ERROR: Could not set permissions on ports");
      return result;
   }

   // This loop will keep running until ctrl-c is pressed
   while (running)
   {
      outb(0xFF, BASE);
      outb(0x00, BASE);
   }

   // Clear permission bits of 4 ports starting from BASE
   result = ioperm(BASE, 4, 0);

   if (result != 0)
   {
      printf("ERROR: Could not clear permissions on ports");
      return result;
   }

   return 0;
}

#include <stdio.h>

#include <inttypes.h>

#include <sys/io.h>

#include <signal.h>

#define BASE 0x378

int running = 1;

void signalHandler(int sig)

{

running = 0;

}

int main(void)

{

printf("Parallel Port Interface Test (Base: 0x%x)n", BASE);

signal(SIGINT, signalHandler);

// Set permission bits of 4 ports starting from BASE

int result = ioperm(BASE, 4, 1);

// If setting permission failed, return

if (result != 0)

{

printf("ERROR: Could not set permissions on ports");

return result;

}

// This loop will keep running until ctrl-c is pressed

while (running)

{

outb(0xFF, BASE);

outb(0x00, BASE);

}

// Clear permission bits of 4 ports starting from BASE

result = ioperm(BASE, 4, 0);

if (result != 0)

{

printf("ERROR: Could not clear permissions on ports");

return result;

}

return 0;

}

User-Mode Access

The code below is the user-mode version. It accesses the parallel port via the ppdev driver. You’ll need to make sure that the driver is compiled into your kernel, or compiled as a module then loaded. The first command below can be used to check if the module is loaded, the second will load it.

> lsmod | grep ppdev
> modprobe ppdev

1 2	> lsmod \| grep ppdev > modprobe ppdev

The ppdev kernel driver can be found in the location shown below.

-> Device Drivers
-> Character Devices
-> <M> Support for user-space parallel port device drivers

-> Device Drivers

-> Character Devices

-> <M> Support for user-space parallel port device drivers

NOTE: Arguments to the ioctl function are passed by pointer, so be careful when using the functions. This is why mode, dir, dataH and dataL are defined first, then their addresses are passed to ioctl.

#include <stdio.h>
#include <sys/ioctl.h>
#include <linux/parport.h>
#include <linux/ppdev.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>

int running = 1;

void signalHandler(int sig)
{
   running = 0;
}

int main(void)
{
   int fd;
   int result;

   printf("Parallel Port Interface Testn");

   // Set ctrl-c handler
   signal(SIGINT, signalHandler);

   // Open the parallel port for reading and writing
   fd = open("/dev/parport0", O_RDWR);

   if (fd == -1)
   {
      perror("Could not open parallel port");
      return 1;
   }

   // Try to claim port
   if (ioctl(fd, PPCLAIM, NULL))
   {
      perror("Could not claim parallel port");
      close(fd);
      return 1;
   }

   // Set the Mode
   int mode = IEEE1284_MODE_BYTE;
   if (ioctl(fd, PPSETMODE, &mode))
   {
      perror("Could not set mode");
      ioctl(fd, PPRELEASE);
      close(fd);
      return 1;
   }

   // Set data pins to output
   int dir = 0x00;
   if (ioctl(fd, PPDATADIR, &dir))
   {
      perror("Could not set parallel port direction");
      ioctl(fd, PPRELEASE);
      close(fd);
      return 1;
   }

   char dataH = 0xFF;
   char dataL = 0x00;

   // This loop will keep running until ctrl-c is pressed
   while(running)
   {
      // Output some data
      // Note that data is passed by a pointer
      ioctl(fd, PPWDATA, &dataH);
      ioctl(fd, PPWDATA, &dataL);
   }

   printf("Shutting downn");

   // Release and close the parallel port
   ioctl(fd, PPRELEASE);
   close(fd);

   return 0;
}

#include <stdio.h>

#include <sys/ioctl.h>

#include <linux/parport.h>

#include <linux/ppdev.h>

#include <fcntl.h>

#include <unistd.h>

#include <stdlib.h>

#include <signal.h>

int running = 1;

void signalHandler(int sig)

{

running = 0;

}

int main(void)

{

int fd;

int result;

printf("Parallel Port Interface Testn");

// Set ctrl-c handler

signal(SIGINT, signalHandler);

// Open the parallel port for reading and writing

fd = open("/dev/parport0", O_RDWR);

if (fd == -1)

{

perror("Could not open parallel port");

return 1;

}

// Try to claim port

if (ioctl(fd, PPCLAIM, NULL))

{

perror("Could not claim parallel port");

close(fd);

return 1;

}

// Set the Mode

int mode = IEEE1284_MODE_BYTE;

if (ioctl(fd, PPSETMODE, &mode))

{

perror("Could not set mode");

ioctl(fd, PPRELEASE);

close(fd);

return 1;

}

// Set data pins to output

int dir = 0x00;

if (ioctl(fd, PPDATADIR, &dir))

{

perror("Could not set parallel port direction");

ioctl(fd, PPRELEASE);

close(fd);

return 1;

}

char dataH = 0xFF;

char dataL = 0x00;

// This loop will keep running until ctrl-c is pressed

while(running)

{

// Output some data

// Note that data is passed by a pointer

ioctl(fd, PPWDATA, &dataH);

ioctl(fd, PPWDATA, &dataL);

}

printf("Shutting downn");

// Release and close the parallel port

ioctl(fd, PPRELEASE);

close(fd);

return 0;

}

Happy Hacking with parallel port!!

Tags: parallel port parallel port in linux parallel port in ubuntu parallel port redhat parallel port suse pport

Parallel port control in Linux

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Parallel port control in Linux

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Examples

Notes

Parallel Port Accessing using C Code

User-Mode Access

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