Chapter 5 - Commissioning
92 3BHS335648 E82 UNITROL 1020 User Manual
5.3.1.20 Communication \ MODBUS (Remote Access)
The RS485 port is shared between VDC mode and MODBUS. With factory settings,
MODBUS is disabled.
To use MODBUS, the parameter MB_Enable must be set to true, then the parameters
have to be written to the EEPROM. Afterwards, the UNITROL 1020 must be restarted.
This procedure has to be followed for any change to MODBUS related parameters to take
effect. It serves as a protection against inadvertently overwriting the setup by MODBUS
itself and therefore losing connection to the UNITROL 1020.
RTU: Protocol of the RS485
Slave ID
Zero and values higher than 247 are reserved, so the valid range for the slave ID is 1 to
247. The default value is 247. Recommended range is 64 to 247 due to the possible
influence with the Modbus ID used for CMT1000 access. For more information refer to
Chapter 3.4.6 – Modbus for Remote Access
Keep-alive time
The parameter “MB_KeepAliveTime” defines in what time-period the “Keep Alive Bit” in
control word 1 must be changed. Valid settings are 1 to 120 seconds and 0 to disable the
connection monitoring.
Keep-alive action
If the timer reaches the supervision time, a “Modbus Communication Alarm” will appear
and one of the events can be selected with the “MB_KeepAliveAction”.
Priority of input signals
All signal assigned to a physical input (digital or analog) cannot be overwritten by modbus
remote acces, and data are ignored
Configurable modbus signals
UNITROL 1020 provides a free configurable signal list to read out required signal with one
access.
Access Levels
Modbus Remote Access shares the control of the AVR with the CMT1000 and the SCP
Panel. The control access has to be granted as explained in Chapter 3.4.7.
For more information, refer to the UN1020 Modbus Reference document, document
number 3BHS348611 E80
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