iSMA-B-MG-IP User Manual
www.ismacontrolli.com
DMP260en | 1st Issue rev. 6 | 05/2022
page 22 of 29
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equipment meters) and a two-wire connecting cable. The slaves are connected in parallel
to the transmission
medium–
the connecting cable.
Figure 16. M-Bus connection topology
A two-wire cable (JYStY N*2*0.8 mm) is used as the transmission medium for the M-Bus.
The maximum distance between the slave and the repeater is 350 m; this length
corresponds to a cable resistance of up to 29
Ω.
This distance applies for the standard
configuration having baud rates between 300 and 9600, and maximum of 250 slaves. The
maximum distance can be increased by limiting the baud rate and using fewer slaves, but
the bus voltage in the space state must at no point fall below 12 V in a segment because
of the remote powering of the slaves. In the standard configuration the total cable length
should not exceed 1000 m in order to meet the requirement of a maximum cable
capacitance of 180 nF.
6.4.2 M-Bus Addressing
M-Bus devices are using two types of addressing:
Primary: this address is assigned by a user in a commissioning process (all new M-Bus
devices have this address, set by default to 0). This type of address has a limited range
from 0 to 250;
Secondary: this address has a wider range than primary and, by default, contains a
device serial number. All out-of-the-box devices connected to the bus have unique
secondary address.
6.5 M-Bus Configuration Registers
6.5.1 Counter of Received Messages (30015)
The 16-bit register with the number of valid M-Bus messages received by the device from
last powering up. The value is reset after a power cycle or after changing transmission
parameters.
6.5.2 Counter of Sent Messages (30017)
The 16-bit register with the number of M-Bus messages sent by the device from last
powering up. The value is reset after a power cycle or after changing transmission
parameters.
WARNING!
Changing the parameters configuring a transmission (except for registers which value
is read from the switch) will only take effect after restarting the device.
