Rockwell Automation 5370 CVIM Communications Manual - Manual (Page 130)

Chapter 5
Using the RS–232 Ports
5–60
/* send DLE STX to initiate message transfer */
_bios_serialcom(_COM_SEND,portnum,DLE);
_bios_serialcom(_COM_SEND,portnum,STX);
/* Send all bytes of the selected command & compute checksum */
for (x=chksum=0; x
{
_bios_serialcom(_COM_SEND,portnum, msg[x]);
chksum += msg[x];
/* If data within the message was 0x10 (a DLE), send another
DLE so the receiver knows it is data, not a control character.
(But don’t include the second DLE in the checksum) */
if (msg[x] == DLE)
_bios_serialcom(_COM_SEND,portnum,msg[x]);
}
/* send DLE ETX and CHKSUM */
_bios_serialcom(_COM_SEND,portnum,DLE);
_bios_serialcom(_COM_SEND,portnum,ETX);
_bios_serialcom(_COM_SEND,portnum,(–chksum)&0xFF);
/* check for DLE ACK */
ch = _bios_serialcom(_COM_RECEIVE,portnum,0);
err = ch & COMMFLAGS;
if (err || ((ch & 0xFF) != DLE)) /* Mask character to 8 bits */
err |= 0x01; /* no DLE on send */
if (!err)
{
ch = _bios_serialcom(_COM_RECEIVE,portnum,0);
err = ch & COMMFLAGS;
/* Mask character to 8 bits
if (err || ((ch & 0xFF) != ACK)) */
err |= 0x02; /* no ACK on send */
}
} while (err && (––retry > 0)); /* if any error, retry */
return (err);
}
/* Receives a message into buffer pointed to by msg & places
length in *len. If the checksum is invalid or a timeout occurs,
sends NAK and attempts to re–receive up to 2 more times.
Returns zero on success or nonzero if an error occurs. */
int get_message (portnum, msg, len)
int portnum; /* Serial port number */
unsigned char *msg; /* Pointer to message buffer */
int *len; /* Pointer to return length of message */
DF1 Programming
Example (cont’d)