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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9.1.4
Specification RS485
Communication speed
300, 600, 1200, 2400, 4800, 9600, 19200, 38400 bps
Communication type
two wire plus extra earth connection
ESD protected to
15 kV
Other
Galvanic isolated from supply earth
9.1.4.1
Failsafe
Some R485 circuits in different products required >200mV between the connections in order to
define the communication levels otherwise there will be a break-signal on the bus. In order to
manage the connection with these circuits/products a failsafe resistance can be needed to get
stable communication.
PiiGAB M-Bus 900S has a built in Failsafe resistance (430Ohm) to boost the limit. Failsafe
resistances are connected via the web interface. If the Failsafe function is activated these will be
connected until they are turned off via the web interface.
By using a Failsafe resistance the current usage is increased which reduces the number of units
on the bus.
PiiGAB M-Bus 900S is using a RS485 implementation that does not require Failsafe. However,
some units on the bus could need Failsafe resistor. Please check this with the product supplier.
9.1.5
Specification RS232
Communication speed
300, 600, 1200, 2400, 4800, 9600, 19200, 38400 bps
ESD protected to
2.5 kV
Other
Galvanic isolated from supply earth
9.1.6
Specification M-Bus Slave
Communication speed
300, 600, 1200, 2400, 4800, 9600, 19200, 38400 bps
Load
One M-Bus load (1.5 mA)
Other
Galvanic isolated from each other and supply earth
9.1.7
Specification M-Bus Master
Communication speed
300, 600, 1200, 2400, 4800, 9600, 19200, 38400 bps
(Normally 300 or 2400 bps)
Voltage ground level (”1”)
40V (±1V)
Voltage zero level (”0”)
28V (±1V)
Short circuit level
280mA
Internal resistance
<100 Ohm
Number of slaves
5/20/60/120 (1.5 mA loads/slave)
