IMST iM871A - Page 14

User Manual
iM871A Wireless M-Bus Module Firmware
iM871A_WMBus_UserManual.docx, Wireless Solutions, v1.2 Page 13
Block 3 to block n (optional blocks):
16 bytes or, if last block, ((L-9) MOD 16) bytes
Data-Field CRC-Field
2 bytes
Figure 3-5: Wireless M-Bus Telegram Format A, block3 to block n
Wireless M-Bus Telegram Format B
Preamble-
sequence
specified by mode 115 bytes
Block 1
Postamble
Block 2
Sync-
word
10 bytes
max. 1 byte126 bytes
Block 3
Figure 3-6: Wireless M-Bus Telegram Format B
Block 1:
L-Field
1 byte 6 bytes1 byte
C-Field M-Field A-Field
2 bytes
Figure 3-7: Wireless M-Bus Telegram Format B, block1 (header)
The first byte of block 1 is the length byte. It describes the number of all following bytes
including the CRC bytes.
The block 1 in Telegram Format B is the same as in Telegram Format A, only the CRC Field
is missing.
Block 2:
CI-Field
1 byte 115 bytes or, if last block, (L-12) bytes
Data-Field CRC-Field
2 bytes
Figure 3-8: Wireless M-Bus Telegram Format B, block2
Block 3 (optional block):
(L-129) bytes
Data-Field CRC-Field
2 bytes
Figure 3-9: Wireless M-Bus Telegram Format B, block3