3.3 Modbus®
Modbus® Protocol Conguration
The time-controlled Modbus® protocol is based on the master-slave working principle.
This means that the substation control and protection system sends an inquiry or
instruction to a certain device (slave address) that will then be answered or carried out
accordingly. If the inquiry/instruction cannot be answered/carried out (e.g.: because of an
invalid slave address), a failure message is returned to the master.
NOTICE!
Some signals (that are active for a short time only) have to be acknowledged separately
(e.g.: trip signals) by the communication system.
The master (substation control and protection system) can query information from the
device, such as:
• Type of unit version;
• Measuring values/statistical measured values;
• Switch operating position (in preparation);
•
State of device;
• Time and date;
• State of the device’s digital inputs; and
• Protection-/state pickups.
The master (control system) can give commands/instructions to the device, such as:
•
Control of switchgear (where applicable, i.e.: each according to the applied device
version);
• Change-over of parameter set;
• Reset and acknowledgment of pickups/signals;
• Adjustment of the date and time; and
•
Control of pickup relays.
For detailed information on data point lists and error handling, please refer to the
Modbus® documentation.
To allow conguration of the devices for Modbus® connection, some default values of the
control system must be available.
Modbus RTU
Part 1: Conguration of the Devices
113www.eaton.comEMR-3MP0
3 Communication Protocols
3.3 Modbus®
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