Question

serial io (c)

Asked by: JohnSpooner

How do you read and write to a serial port under Linux?
Where can I find examples?  I am new to Linux and my reference books dont mention serial io at all.  Under windows the steps were:
1.  configure the port.
2.  open a file corresponding to the port
3.  write a read thread that looped about endlessly hoping for input.

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Asked On
2000-12-06 at 07:43:35ID20000488
Tags

serial

,

io

,

linux

Topic

Linux Programming

Participating Experts
3
Points
200
Comments
11

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Related Solutions

  1. serialization?
    what is serialization? i've heard this term many times but i have no idea what it is :)

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Answers

 

by: JohnSpoonerPosted on 2000-12-06 at 08:03:04ID: 981

let me know if this is a harder qustion than i think

 

by: akehPosted on 2000-12-06 at 08:54:29ID: 1021

 

by: JohnSpoonerPosted on 2000-12-06 at 14:52:05ID: 1332

so its not as simple as an example program (as it is in windows).  i looked and looked
and i didnt see any code on this site.

 

by: JohnSpoonerPosted on 2000-12-06 at 21:19:20ID: 1766

my mistake, i found some code.  

 

by: jittulPosted on 2000-12-08 at 21:08:21ID: 4653

Hi,
The details of serial programming are avilable on your Linux itself.see the HOWTO pages in /usr/doc .in this,you'll find something called serialprogramming-HOWTO.you'll find sample code in it,with explanation.How to use the termois structure,how to set the attributes of a serial port,etc.,.
In Linux,the steps to follow are:
1)Check the Serial device(eg./dev/ttyS1),wether free or not.
2)If free,open the port and set the attributes using functions tcgetattr and tcsetattr,use the port.
3)Close the port after done.

Thanx ;-)
Jit

 

by: JohnSpoonerPosted on 2000-12-10 at 22:12:33ID: 8520

Yes, I found it and it works on ttyS0 and ttyS1!
(sorry but my connection to e exchange is super slow
or i would have responded quicker)

now i am trying to figure out how to get
ttyS2 and ttyS3 to work as well.

should i count this question as answered since i didnt
mention com3,com4 before?


 

by: jittulPosted on 2000-12-11 at 21:47:35ID: 10325

Hi there,
There is no change in program for ttyS2(COM2) and ttyS3(COM3) as the only thing you have to change is the device name you pass to the file descriptor.
you say:
fd = open("/dev/ttySx",O_RDWR|O_NOCTTY);

where the device can be any one of avilable serial ports.
Thanx
Jit

 

by: JohnSpoonerPosted on 2000-12-12 at 08:32:30ID: 11406

yes.  i am passing variously:
  ttyS0,ttyS1,tyS2,ttyS3

S2 and S3 do not recieve data.  so i am looking at the jumoer settings and decipering the gett attributes command

 

by: jittulPosted on 2000-12-12 at 23:32:29ID: 13841

Hi,
Let me make one point clear to you.There will be problems sometimes in setting the baud rate for the port.any way you'll set it in the termois structure but i recommend you to use the function 'tcsetospeed'.to set the baud rate again.
Thanx
Jit

 

by: JohnSpoonerPosted on 2000-12-13 at 05:55:35ID: 14871


i used setserial to change the iq's for ttyS2 and ttyS3 and now all 4 ports are working.
In the HOWTO pages I found a warning that this might be needed for the 'other' com ports.

the example program sets baudrate and other characterstics in the terminal io structure.

 

by: sarmadysPosted on 2000-12-18 at 14:30:33ID: 30166

Hi

This is a sample program for setting your comport.
Then you will be able to write to habdle( global var )

Sincerely, Siamak


static void CommunicationSetting(){
    struct termios tio ;
    int  i ;
    unsigned char buf[30];
    char TMP[50],TMP1[20];

    i=0;
    sprintf( buf, "/dev/tty%da", Data.Config.Settings.ComPort ) ;

    portHandle= open( buf, O_RDWR| O_NONBLOCK| O_NOCTTY) ;

    if( portHandle==-1 )
         {
          perror( buf) ;
          CONP_("\nDaemon : Error in communication port !");
          return ;
         }
       
    tcgetattr( portHandle, &tio) ;

    sprintf(TMP,"\n\n\n\nprevline attribute: %o\t%o\t%o\t%o\n", tio.c_iflag, tio.c_oflag, tio.c_cflag, tio.c_lflag ) ;
    CONP_(TMP);

    i =tio.c_cflag & 00777760 ;
   
    i |=B2400 |  CSTOPB | CS8 ;
         
     i &= ~(CLOCAL) ;
     tio.c_cflag = i;
     tcsetattr( portHandle, TCSANOW, &tio) ;
 
     tcgetattr( portHandle, &tio) ;
 
     sprintf(TMP, "\n\n\n\n(%s)line attribute: %o\t%o\t%o\t%o\n",TMP1, tio.c_iflag, tio.c_oflag, tio.c_cflag, tio.c_lflag ) ;
     CONP_(TMP);        
}

20120131-EE-VQP-002

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