T H E M O D E R M - B U S T E C H N O L O Y
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7.2
Communication tips
7.2.1
Correct baud rate
The baud rate which is set via the web interface must agree with the m
eter’s baud rate. Some
meters are set at a baud rate of 300bps at delivery. If possible try to set the meters to 2400bps
to increase the baud rate and the performance. When communication with the meters is
established you can continue to configure the superior software.
7.2.2
The meter’s board rate settings
It is possible to control the meter on the M-Bus network directly in the M-Bus Wizard via primary
and secondary addressing. It is also possible to adjust the basic settings such as baud rate and
primary addres
sing via the network. Please note that some meter manufacturers don’t support
the possibility to change for example the primary address or the baud rate via the standard M-
Bus commands.
7.2.3
Supplier specific configuration software
If you want to configure th
e meters via the supplier’s own software it is normally possible to do
so via a free slave port on the gateway.
7.2.4
Parameter settings to keep in mind
A few key points to keep in mind concerning the communication between the meter and the
superior software.
7.2.4.1
Time interval between the questions
Since the M-
Bus protocol is a slow protocol the questions shouldn’t be asked too often to the
meters.
7.2.4.2
The number of telegrams that can be read out from the meter
If you have a meter that contains many telegrams a so called multi telegram meter make sure
not to read more telegrams than necessary. With client software from PiiGAB it is possible to set
the parameter NrOfTelegrams, which limits the number of M-Bus telegrams read from the
current meter.
7.2.4.3
Baud rate
Baud rate 2400 Baud which is the same as 2400 bits per second is the most common baud rate
for M-Bus. If you have a meter with the max length of 261 bytes from a meter this corresponds
approximately to 2600 bites. With a baud rate of 2400 Baud a reading like that would take more
than a second.
For 300 Baud this corresponds to 2600/300 which is approximately eight seconds. In other
words try to avoid 300 baud as much as possible. Please note that there will be additional time
for the question itself as well as the adaptation in the meter.
Some meters have up to 40 telegrams that can be read out. With a baud rate of 300 bps this
will take a very long time.