Fc6 - Write Single Register; Fc16 - Write Multiple Registers; Exception Responses - Siemens SINAMICS V20 Operating Instructions Manual

FC6 - Write Single Register

When a message with FC = 0x06 is received, then 4 bytes of data are expected, that is, FC6
has 4 bytes of data:
● 2 bytes for the starting address of register
● 2 bytes for the register value
Byte 1 Byte 2
Address FC (0x06)
Inverter response
Byte 1 Byte 2
Address FC (0x06)

FC16 - Write Multiple Registers

When a message with FC = 0x10 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 of register
● 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 Start address
(0x10)
High
Inverter response
Byte 1 Byte 2
Address FC (0x10)

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.
SINAMICS V20 Inverter
Operating Instructions, 09/2014, A5E34559884
Byte 3 Byte 4
Start address
High Low
Byte 3 Byte 4
Start address
High Low
Byte 4 Byte 5 Byte 6
Number of regis-
ters
Low High Low
Byte 3 Byte 4
Start address
High Low
Byte 5 Byte 6
New register value
High Low
Byte 5 Byte 6
New register value
High Low
Byte 7 ... Byte N -
1
Number ... Register N value
of bytes
High
Byte 5 Byte 6
Number of registers
High Low
Communicating with the PLC
6.2 MODBUS communication
Byte 7 Byte 8
CRC
High Low
Byte 7 Byte 8
CRC
High Low
Byte N Byte N + Byte N +
1 2
CRC
Low High Low
Byte 7 Byte 8
CRC
High Low
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