Why do I get the error "Missing value" when reading some M-Bus devices?

FAQ #101762

 

Symptom
When using the M-Bus modules PCD2/3.F27xx (with the framing protocol), the M-Bus driver may display the error "Missing value" even though all values are correctly returned. The problem concerns only few devices; so far the following concerned devices are known:

• Janitza, electricity counter
• EMU Professional, electricity counter
• L&G Ultraheat 50, heating counter

Reason
This problem occurs because the PCD firmware (older than 1.16.66) looses some bytes if the reply telegrams is longer than 240 bytes (and the framing protocol is used).

Solution
This problem is corrected in the PCD firmware version 1.16.66 and later. This firmware is e.g. contained in the BACnet firmware package available on the Support Site (under "Communication Protocols" --> "BACnet")