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MessengerBLE
User Guide
7
Modbus
The Messenger can be configured as a Modbus Master, Modbus Slave or both. This is
done by setting the Mode of one of the available user serial ports, 5 or 6. Both ports
support RS485 only. If RS232 is required, an RS485 to RS232 adapter will need to be
inserted.
7.1
RTU Slave
Being configured as a Modbus RTU Slave device allows SCADA/HMI software to read
channel values from the Messenger. Setting up a serial port is the only configuration
necessary to enable Modbus Slave operation.
Also available is writing values to the Messenger from a MODBUS Master. These
written values can then be transferred to a channel for alarming or logging for
telemetry.
The Modbus register map for all channel data values is available on request. Reference
document number “Messenger MODBUS Slave Register Map”.
7.2
RTU Master
When configured as a Modbus RTU Master device, the Messenger reads register
values from Modbus Slave devices.
In addition to setting up a Modbus Master serial port, the MODBUS data registers in
the Messenger must be configured to receive the values read from the slave device. In
Channel Configuration
, define the Modbus Slave address, the register data type to
read, the register number, how to interpret or scale the data being read, and any
alarm limits.