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MBUS User Manual (ver 2.01)
MBUS USER MANUAL
When setting DATA_INTERFACE = 1, the received HEADER will not be sent on the UART (typically used on a
slave). However, to be able to notify the external application when an Acknowledg
ement is received (“empty”
frame), a special string can be used. By setting DATA_INTERFACE = 3, the two byte string 00:E5h (i.e. L = 0) will
be sent on the UART when an empty acknowledge frame is received.
Application data (CI + APPL_DATA) is always present (except when only a HEADER is received).
For host applications using a UART buffer the timing information used for parsing could be lost. In this case a start
and stop byte can be used. Setting DATA_INTERFACE = 4 will add a START byte (68h) and a STOP byte (16h) to
the message. This is only used for the module-to-host communication direction (TXD). Setting DATA_INTERFACE
= 8 will add a two byte CRC checksum, and DATA_INTERFACE = 0Ch will add START/STOP bytes and CRC. The
CRC is sent MSByte first.
The RSSI value is appended when RSSI_MODE = 1.
2.4 Network Topology
A Wireless M-Bus supported metering system normally consists of a number of heat-, gas-, water and/or electricity
meters which reports their meteorological readings to a concentrator. The concentrator acts as the Master in the
system while the meters are Slaves. In the standard the Master is referred to as “Other”.
The Radiocrafts Wireless M-Bus family of modules can be configured to have a role as either Master or Slave. The
Slave contains a unique address, and when sending a meter reading this address is added to the wireless
message. The message from a Slave does not contain any Master address but the Master module within range will
receive the message, and based on the Slave address (if the Slave is installed and the Master is configured for
filtering), it will decode the message and send the data on its serial interface (TXD-pin).
In two-
way communication modes, the battery operated meter (slave) will keep the receiver “on” for a short time.
During this time slot the master can acknowledge the received message in order to open the communication
channel (NTA 8130), or send a command (OMS) and thereby start a communication sequence.
MBUS3 (OMS) and MBUS4 also allows for a one-way (unidirectional) repeater. The repeater will re-transmit all
messages from slaves within range. Modules with MBUS3 and MBUS4 feature sets can be configured as a
repeater.
MBUS3 has since its original release been extended to support the new C-mode (Compact mode), in addition to
OMS functionality. A unique feature of MBUS3 is that T mode and C mode messages can be received in parallell
with the same configuration.
For battery operated devices the slave is always initiating the communication, and the master must then transmit (if
need) within a short time window (2-
3 ms in the T mode). After one such “ping-pong” sequence, the slave will have
a pause (enter sleep mode) for 2-5 seconds, before it again do a new transmission allowing the master to do
another transmission. This means that all messages to be sent from the master must be ready and transmitted
within a very short time. The MBUS3 Auto-message generator and Mailbox features make this task easy and
doable (patented implementation).
MBUS3 supports 64 slaves registered in a master.
MBUS3 also support reception of mode C. Mode C can be received in combination with mode T. The module also
automatically receives and distinguish between Frame Format A and B. The current implementation supports C1
mode (unidirectional) as specified in the EN 13757-4 (2013). The timing of C2 mode is currently not supported. C
mode meters can be installed in the Master module, optionally with encryption keys, mixed with T mode meters.
