Siemens SINAMICS V90 Operating Instructions Manual page 209

For the Modbus data format, V90 supports Modbus RTU while Modbus ASCII is not
supported. Registers of the servo drive can be read by Modbus function code FC3 and
written via Modbus function code FC6 (single register) or FC16 (multiple registers).
Supported function codes
The SINAMICS V90 supports only three function codes. If a request with an unknown
function code is received, an error message will be returned.
FC3 - Read holding registers
When a message with FC = 0x03 is received, then four bytes of data are expected, that is,
FC3 has four bytes of data:
● Two bytes for the starting address
● Two bytes for the number of registers
Byte 1
Address
FC6 - Write single register
When a message with FC = 0x06 is received, then four bytes of data are expected, that is,
FC6 has four bytes of data:
● Two bytes for the register address
● Two bytes for the register value
Byte 1
Address
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:
● Two bytes for the starting address
● Two bytes for the number of registers
● One byte for the byte count
● N bytes for the register values
Byte 1
Ad-
dress
SINAMICS V90, SIMOTICS S-1FL6
Operating Instructions, 09/2016, A5E36037884-002
Byte 2 Byte 3
FC (0x03) Start address
High
Byte 2 Byte 3
FC (0x06) Start address
High
Byte 2 Byte 3 Byte 4
FC Start address
(0x10)
High Low
Byte 4 Byte 5
Number of registers
Low High
Byte 4 Byte 5
New register value
Low High
Byte 5 Byte 6 Byte 7
Number of regis- Num-
ters ber of
bytes
High Low
Control functions
7.7 Communicating with the PLC
Byte 6 Byte 7
CRC
Low High
Byte 6 Byte 7
CRC
Low High
Byte 7 Byte 8 Byte 9
+ N + N + N
Register N value CRC
High Low High
Byte 8
Low
Byte 8
Low
Byte
10 + N
Low
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