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Full Discussion: Writing to a Serial Port
Top Forums Web Development Writing to a Serial Port Post 302920183 by Meow613 on Wednesday 8th of October 2014 12:28:22 AM
Old 10-08-2014
Writing to a Serial Port

I am trying to write to a serial port and capture the reponse in a file -

Code:
adduser ethan dialout 
The user `ethan' is already a member of `dialout'
root@meow:/home/ethan# ls -l /dev/ttyS0
crw-rw-r-- 1 ethan dialout 4, 64 Oct  7 20:55 /dev/ttyS0

$fh1 = fopen("/dev/ttyS0", "w+");
fwrite($fh1, "W\n"); //This sends a signal to a scale to return the weight of an object
fread($fh1, 100);
echo $fh1;

If I run this code -


Warning: fopen(/dev/ttyS0): failed to open stream: Permission denied in /var/www/TestScale.php on line 20

Warning: fwrite() expects parameter 1 to be resource, boolean given in /var/www/TestScale.php on line 21

Warning: fread() expects parameter 1 to be resource, boolean given in /var/www/TestScale.php on line 22

TIA
 

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FREAD(3)								 1								  FREAD(3)

fread - Binary-safe file read

SYNOPSIS
string fread (resource $handle, int $length) DESCRIPTION
fread(3) reads up to $length bytes from the file pointer referenced by $handle. Reading stops as soon as one of the following conditions is met: o$length bytes have been read o EOF (end of file) is reached o a packet becomes available or the socket timeout occurs (for network streams) o if the stream is read buffered and it does not represent a plain file, at most one read of up to a number of bytes equal to the chunk size (usually 8192) is made; depending on the previously buffered data, the size of the returned data may be larger than the chunk size. PARAMETERS
o $handle -A file system pointer resource that is typically created using fopen(3). o $length - Up to $length number of bytes read. RETURN VALUES
Returns the read string or FALSE on failure. EXAMPLES
Example #1 A simple fread(3) example <?php // get contents of a file into a string $filename = "/usr/local/something.txt"; $handle = fopen($filename, "r"); $contents = fread($handle, filesize($filename)); fclose($handle); ?> Example #2 Binary fread(3) example Warning On systems which differentiate between binary and text files (i.e. Windows) the file must be opened with 'b' included in fopen(3) mode parameter. <?php $filename = "c:\files\somepic.gif"; $handle = fopen($filename, "rb"); $contents = fread($handle, filesize($filename)); fclose($handle); ?> Example #3 Remote fread(3) examples Warning When reading from anything that is not a regular local file, such as streams returned when reading remote files or from popen(3) and fsockopen(3), reading will stop after a packet is available. This means that you should collect the data together in chunks as shown in the examples below. <?php // For PHP 5 and up $handle = fopen("http://www.example.com/", "rb"); $contents = stream_get_contents($handle); fclose($handle); ?> <?php $handle = fopen("http://www.example.com/", "rb"); if (FALSE === $handle) { exit("Failed to open stream to URL"); } $contents = ''; while (!feof($handle)) { $contents .= fread($handle, 8192); } fclose($handle); ?> NOTES
Note If you just want to get the contents of a file into a string, use file_get_contents(3) as it has much better performance than the code above. Note Note that fread(3) reads from the current position of the file pointer. Use ftell(3) to find the current position of the pointer and rewind(3) to rewind the pointer position. SEE ALSO
fwrite(3), fopen(3), fsockopen(3), popen(3), fgets(3), fgetss(3), fscanf(3), file(3), fpassthru(3), ftell(3), rewind(3). PHP Documentation Group FREAD(3)
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