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Re: [ts-7000] 485 half duplex communication error

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Subject: Re: [ts-7000] 485 half duplex communication error
From: Jim Jackson <>
Date: Thu, 7 Feb 2013 19:58:20 +0000 (GMT)


On Thu, 7 Feb 2013, khouryelie wrote:

> 
> i tried dissaserting rts with the following code 
> 
>         int fd;
>         int status;
> 
>       fd = open("/dev/tts/4", O_RDWR | O_SYNC);
>       if (fd == -1) 
>       {
>               perror("Error opening file for writing");
>       }
> 
>         ioctl(fd, TIOCMGET, &status);
> 
>         status &= ~TIOCM_RTS;
> 
>         ioctl(fd, TIOCMSET, &status);
> 
> stil no reading
> 

2 points

   1 - sloppy coding  - you are not checking the returned value from the 
       ioctl. If the call to ioctl does not return 0 then there was an 
       error. Your code maybe failing.

   2 - This code should have a physical effect - the RTS line on the
       interface should go from high to low (in rs232 that would be from a 
       high voltage to a negative voltage). Have you measured it? Did it do 
       what was expected?


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