Modbus Communication - Siemens SINAMICS V90 Operating Instructions Manual

7.7.2

Modbus communication

The SINAMICS V90 servo drive can communicate with the PLC through an RS485 cable
with the standard Modbus communication protocol. For 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 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
SINAMICS V90, SIMOTICS S-1FL6
Operating Instructions, 07/2015, 6SL3298-0AV60-0BP0
Byte 2 Byte 3
FC (0x03) Start ad-
dress
(most
significant
byte)
Byte 2 Byte 3
FC (0x06) Start ad-
dress
(most
significant
byte)
Byte 4 Byte 5
Start ad- Number of
dress registers
(least (most
significant significant
byte) byte)
Byte 4 Byte 5
Start ad- New regis-
dress ter value
(least (most
significant significant
byte) byte)
Control functions
7.7 Communicating with the PLC
Byte 6 Byte 7
Number of CRC
registers
(least
significant
byte)
Byte 6 Byte 7
New regis- CRC
ter value
(least
significant
byte)
Byte 8
CRC
Byte 8
CRC
185