Rockwell Automation 1771-DMC_DMC1_DMC4_DXPS Control Coprocessor User Manual - Manual (Page 122)

Chapter 7
Using the Serial Ports
7-14
* NOTE: Always use a _gs_rdy() call to make sure there are
* is enough data to read in the input buffer before making
* this read call. Otherwise the function will appear to
* ’hang’, because it is waiting for the number of characters
* it was told to read.
* SYNOPSIS int read_485(path, buffer, count)
* int path; - Path number from opened port
* char *buffer; - Pointer to buffer for read
* int count; - minimum size of buffer
* EXAMPLE: int path;
* char in_data[10];
* int cnt = 5;
* path = open(“/t1”, (S_IREAD | S_IWRITE));
* init_485(path);
* status = read_485(path, in_data, cnt)
* if (status == -1)
* exit();
****************************************************************************/
int read_485(path, buffer, count, timeout)
int path;
char *buffer;
int count;
int timeout;
{
int status;
int tmp_count=0;
/*** Make sure there is enough data in input buffer before reading ***/
while (((tmp_count = _gs_rdy(path)) < count) && timeout--)
;
/*** Ooops, timeout. No data. Returning. ***/
if (timeout == -1)
{
fprintf(stderr, “**** ERROR timeout in read_485() function! ***\n”);
return(-1);
}
/*** Do the read since there is data there ***/
status = read(path, buffer, count);
return(status);
}
/*****************************************************************************
* w r i t e _ 4 8 5 . c
* PURPOSE: Write characters to a serial port configured for RS-485.
* REVISION LOG: 4/12/94 Original release of program
* USAGE: This function writes characters to a port configured for RS-485.
* Because doing serial write commands over RS-485 requires special
* techniques to complete the write, this function was created to
* take care of the details of transmitter control and the clearing
* of the input buffer.
* Function returns the number of bytes actually written. A -1 is
* returned if an error occurs. The error code is placed in the
* variable ’errno’. The function will no return until all the
* characters are physically transmitted out of the port.
* SYNOPSIS int write_485(path, buffer, count)
* int path; - Path number from opened port
* char *buffer; - Pointer to write buffer
* int count; - minimum size of buffer