Limitations#

T Mode Meter to Other Device (only for EFR32 Series 1)#

While the hardware supports 3 out of 6 coding, EFR32 Series 1 cannot generate the postamble required by this mode (this does not matter in receive mode). For T Mode Meter to Other transmission on EFR32 Series 1, we recommend using the supplied encoder function (WMBUS_phy_software()), which calculates the CRC using the GPCRC peripheral, encodes the packet using a software based 3 out of 6 encoder, and adds the required postamble.

On EFR32 series 2, where Wireless M-Bus support is available (e.g. EFR32xG23), this feature is available from hardware. The software workaround is no longer recommended.

Select Frame Type Based on Sync Word#

Modes C, N, and F support frame formats A and B, where the sync word selects the frame format. Receiving frame A and frame B with the same configuration is currently not supported. You can either:

  • Set up the frameA configuration and receive only frame format A.

  • Set up the frameB configuration and receive only frame format B.

  • Manually create a multi-PHY configuration and switch between the configurations at runtime. However, you must decide which frame you expect before you switch to RX mode.

  • Set up a custom C/N/F configuration with no frame coding option. In that case, you must decode the length and check CRC in software, but you can decide the frame type during reception as well.

Modes that support frame format B always have both sync words configured:

  • FrameA and noFrame configurations have sync word 0 configured for frame type A and sync word 1 for type B.

  • FrameB configurations have sync word 0 configured for frame type B and sync word 1 for frame type A.

You cannot receive frame type B with a frameA configuration or vice versa, but you can enable the second sync word in RAIL, and use the sync detect event to recognize that you are receiving something with the other frame type.

Decoder for Both C and T Mode Meter to Other#

It is theoretically possible to receive mode C frames with a mode T configuration, because the first 10 bits of the sync word are the same. If the next 6 bits are a valid 3 out of 6 code, it is a T frame, and if the next 16 bits are the second part of mode C’s sync word, it is a C frame. Since the second part of mode C’s sync word is not a valid 3 out of 6 code, it is not possible that both conditions are true for a correctly formatted frame.

With the WMbus TC M2O (100k, frameA) PHY, it is possible to receive mode T and mode C packets. When transmitting, this PHY always uses mode T. The RAIL_WMBUS_Config API can be used to enable the simultaneous RX option which makes it possible to receive mode C frame A/B and mode T frame type A packets.

Note, that with the T+C mode PHY, performance cannot be guaranteed. The PHY is based on the mode T PHY, so it should match the mode T performance, but this specific mode was not characterized.