Siemens SINAMICS V20 Series Operating Instructions Manual page 110

Communicating with the PLC
6.2 MODBUS communication
FC6 - Write Single Register
When a message with FC = 0 x 06 is received, then 4 bytes of data are expected, that is,
FC6 has 4 bytes of data:
● 2 bytes for the register address
● 2 bytes for the register value
Byte 1 Byte 2
Address FC (0 x 06)
FC16 - Write Multiple Registers
When a message with FC = 0 x 10 is received, then 5 + N bytes of data are expected, that
is, FC16 has 5 + N bytes of data:
● 2 bytes for the starting address
● 2 bytes for the number of registers
● 1 byte for the byte count
● N bytes for the register values
Byte 1 Byte 2 Byte 3
Address FC (0 x Start
10) address
(MSF)
Exception Responses
If an error is detected through the MODBUS processing, the slave will respond with the FC
of the request, but with most significant bit of the FC high and with the Exception Code in the
data field. However, any error detected on the global address 0 does not result in a response
since all slaves cannot respond at once.
If an error is detected within the received message (for example, parity error, incorrect CRC
and so on), then NO response is sent to the master.
Note that if a request with FC16 is received which contains a write that the inverter cannot
perform (including write to a zero entry), other valid writes will still be performed even though
an exception response is returned.
The following MODBUS Exception Codes are supported by SINAMICS V20:
Exception Code
01
02
03
04
110
Byte 3 Byte 4
Start address Start address
(MSF) (LSF)
Byte 4 Byte 5
Start Number
address of
(LSF) registers
(MSF)
MODBUS name
Illegal function code
Illegal data address
Illegal data value
Slave device failure
Byte 5 Byte 6
New register New register
value (MSF) value (LSF)
Byte 6 Byte 7 Byte 7 +
n
Number Number nth value
of of bytes (MSF)
registers
(LSF)
Meaning
The function code is not supported – only FC3,
FC6 and FC16 are supported.
An invalid address was queried.
An invalid data value was recognized.
An unrecoverable error occurred while the device
was processing the action.
Byte 7
CRC
Byte 8 + Byte 9 +
n n
nth value CRC
(LSF)
SINAMICS V20 Inverter
Operating Instructions, 07/2012, A5E03728167
Byte 8
CRC
Byte 10
+ n
CRC