4. MODBUS COMMUNICATION PROTOCOL
IMR02F04-E1
38
4.7 Caution for Handling Communication Data
The numeric range of data used in Modbus protocol is 0000H to FFFFH. Only the set value within the
setting range is effective.
FFFFH represents
1.
The Modbus protocol does not recognize data with decimal points during communication.
Example: When Measured value (PV) is 5.0 MPa,
5.0 is processed as 50,
50 = 0032H
Measured value (PV)
High
00H
Low
32H
If data (holding register) exceeding the accessible address range is accessed, an error response
message is returned.
Read data of unused item is a default value.
Any attempt to write to an unused item is not processed as an error. Data cannot be written into an
unused item.
If data range or address error occurs during data writing (Write Action), it is not processed as an error.
Normal data is written in data register but data with error is not written; therefore, it is recommended
to confirm data of changed items after the data setting.
An attribute of the item for functions which are not in the indicator is RO (read only). If read action to
this item is performed, the read data will be “0.” If write action to this item is performed, no error
message is indicated and no data is written.
Commands should be sent at time intervals of 30 bits after the master receives the response message.
