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CM 1241 (RS232) CRC Error Check

7/5/2010 7:01 AM	Rate (0)
enookway Posts: 3 Rating: (0)	I am configuring a CM 1241 to send packet data to a third party device. Part of the message structure is to include a CRC16 error check at the end of each packet. 1. Is there a built in facility in the CM 1241 to include CRC error checking? 2. If not, is there a method of programming CRC in Ladder or other programming language? Any examples would be much appreciated Ian
enookway Posts: 3 Rating: (0)
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7/5/2010 3:39 PM	Rate (0)
Denilson Pegaia Platinum Member Joined: 9/23/2005 Last visit: 3/21/2025 Posts: 4406 Rating: (1475)	Hi, This type of CRC is used in MODBUS communication. Are you using MODUBS communications?
	Denilson Pegaia Siemens Industry Sector Technical Support
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7/9/2010 6:21 AM	Rate (0)
enookway Posts: 3 Rating: (0)	No, not using Modbus. Simply using a SEND_PTP via an RS232 module. The packet structure I need to send will look like this (each < > represents one byte of data): <preamble><Data byte 1><Data byte 2>..........<Data byte 11><CRC16 code><CRC16 code> I have the structure working except for the 2 CRC bytes at the end. Project attached. If I were to use Modbus, can I customise the structure to the length I need (12 bytes of data followed by two bytes of CRC). I have looked at the example projects posted here for Modbus RTU but I am struggling with how the data packet is put together and how the message length works. Using the S7-1200 to send to a terminal program shows that each message consists of 5 bytes and appears to be sent 3 times for every send request. Any message length above 7 stops transmission. I am obviously missing something fundamental about modbus. Attachment RS232 100705-2.zip (239 Downloads)
enookway Posts: 3 Rating: (0)
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