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Modbus services
S1A53844 01/2011 33
Modbus functions available
The following table indicates which Modbus functions are managed by the Altivar 212 and specifies their limits.
The "read" and "write" functions are defined from the point of view of the master.
Read one word (03)
Function 3, quantity = 1
One word function permits to read one parameter value. All parameter of the Altivar 212 can be read.
Request:
Response:
Error response:
Example: Read [Output frequency] (
Fd00) on Altivar 212 at slave address 1
Request:
Response:
Example: Invalid read of 2 words
Request:
Error response:
Code Function name Size of data Altivar 212 function name Broadcast
3 = 16#03 Read Holding Registers 1 object Read one word Yes
1 ... 5 objects Read indirect block Yes
6 = 16#06 Write Single Register 1 objects Yes
16 = 16#10 Write Multiple Registers 1 object Write one word Yes
2 objects Write indirect block Yes
43/14 = 16#2B/0E Read Device Identification 3 objects No
Slave no. Function code Starting address Quantity of registers
(fixed)
CRC16
03
Hi Lo 00 01 Lo Hi
1 byte 1 byte 2 bytes 2 bytes 2 bytes
Slave no. Function code Byte count Register value CRC16
03
Hi Lo Lo Hi
1 byte 1 byte 1 byte 2 bytes 2 bytes
Slave no. Function code Exception
code
CRC16
83 Lo Hi
1 byte 1 byte 1 byte 1 byte 1 byte
01 03 FD 00 00 01 B5 A6
01 03 02 17 70 B6 50
01 03 FD 00 00 02 F5 A7
01 83 03 01 31