Data access using the Modbus RTU protocol
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isoGEN523_D00320_04_M_XXEN/06.2018
7.2.1
Command of the master to the ISOMETER®
In this example, the master addresses the ISOMETER® with address 3 and requests
that the content of the register with address 3003 is set to 2.
7.2.2
The ISOMETER® answers the master
7.3 Exception code
If a request cannot be answered for whatever reason, the ISOMETER® will send a so-
called exception code with which possible faults can be narrowed down.
Byte Name Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x10
Byte 2, 3
Start register
0x0BBB
Byte 4, 5
Number of registers
0x0001
Byte 6
Number of data bytes
0x02
Byte 7, 8
Data
0x0002
Byte 9, 10
CRC16 Checksum
0x9F7A
Byte Name Example
Byte 0
ISOMETER® Modbus address
0x03
Byte 1
Function code
0x10
Byte 2, 3
Start register
0x0BBB
Byte 4, 5
Number of registers
0x0001
Byte 6, 7
CRC16 Checksum
0x722A
Exception code
Description
0x01 Impermissible
function
0x02
Impermissible data access
0x03
Impermissible data value
0x04 Internal
fault
0x05 Acknowledgement
of
receipt
(answer will be time-delayed)
0x06
Request not accepted (repeat request if necessary)
