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AN017: CRC CALCULATIONSFOR MBUS MODULES
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APPLICATION NOTE: AN017
2017 Radiocrafts AS Application Note AN017 (rev. 1.1)
CRC Calculations for MBUS Modules By H.Moholdt
Introduction
The Wireless M-Bus modules (MBUS3, MBUS4) from Radiocrafts can be enabled with CRC-16 for possible
error identification on the UART port. This feature secures that the data handling on the serial interface is
more secure as wrong data can be rejected.
CRC Introduction
Enter config mode and send M-command and sequence ‘0x51 0x04 0xFF’, then exit config mode via X.
The CRC calculation is referenced in FT3 of EN60870-5-1, the same as used in Wireless M-Bus. It uses the
following generator polynomial;
x16+ x13+ x12+ x11+ x10+ x8+ x6+ x5+ x2+ x0
The initial value is 0x0000, the polynomial is 0x3D65 as shown above, and the result is inverted. The most
significant byte of the 16-bit CRC is transmitted first.
To calculate the CRC manually, several online programs can be used, like for instance
http://zorc.breitbandkatze.de/crc.html which returns a CRC result for a Wireless M-bus telegram. The data
sequence can be manually entered into the program and the coded result will be displayed.
CRC handling on MBUS UART
The message from the module’s UART (which it is sending to the host), with UART CRC enabled in DATA_INTERFACE, is calculated from and including the original length byte (excl the two CRC bytes), to and including the RSSI append byte (if enabled). Start/stop bytes (if enabled) are not included in the CRC calculation, and not the CRC bytes itself. Thus, the following general procedure applies to a received UART-message from a module where CRC is enabled; -Remove the start/stop byte(s) -Remove the two CRC bytes and reduce the length byte by 2 -Then calculate the CRC over the remaining frame (including any RSSI), starting with the length byte -Invert the result -Compare with the received CRC.
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APPLICATION NOTE: AN017
2017 Radiocrafts AS Application Note AN017 (rev. 1.1)
Document Revision History
Document Revision Changes 1.0 First release
1.1 Design Update
Disclaimer
Radiocrafts AS believes the information contained herein is correct and accurate at the time of this printing. However, Radiocrafts AS
reserves the right to make changes to this product without notice. Radiocrafts AS does not assume any responsibility for the use of
the described product; neither does it convey any license under its patent rights, or the rights of others. The latest updates are available
at the Radiocrafts website or by contacting Radiocrafts directly.
As far as possible, major changes of product specifications and functionality, will be stated in product specific Errata Notes published
at the Radiocrafts website. Customers are encouraged to check regularly for the most recent updates on products and support tools.
Trademarks
RC232™ is a trademark of Radiocrafts AS. The RC232™ Embedded RF Protocol is used in a range of products from Radiocrafts. The
protocol handles host communication, data buffering, error check, addressing and broadcasting. It supports point-to-point, point-to-
multipoint and peer-to-peer network topologies.
All other trademarks, registered trademarks and product names are the sole property of their respective owners.
Life Support Policy
This Radiocrafts product is not designed for use in life support appliances, devices, or other systems where malfunction can
reasonably be expected to result in significant personal injury to the user, or as a critical component in any life support device or
system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its
safety or effectiveness. Radiocrafts AS customers using or selling these products for use in such applications do so at their own risk
and agree to fully indemnify Radiocrafts AS for any damages resulting from any improper use or sale.
© 2017, Radiocrafts AS. All rights reserved.
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