Siemens SINAMICS V20 Operating Instructions Manual page 184

Communicating with the PLC
7.2 MODBUS communication
Reading and writing parameters acyclically
Via FC16, with one request, up to 122 registers can be written to directly one after the other;
while for Write Single Register (FC6) you must individually write the header data for each
register.
Header
In addition to the slave address, enter the transfer type, the start address and the number of
the following registers in the header.
User data
You control the access in the user data via register 40601.
In register 40602, you define the acyclic access as well as the length of the request data.
Register 40603 contains the request reference - it is defined by the user - and the access
type -reading or writing.
Register 40604 contains the number of the drive object (always 1) and the number of
parameters that are read or written.
Register 40605 contains the attribute that you use to control whether you read out the
parameter value or the parameter attribute. In the number of elements you specify how many
indices are read.
Example: r0002 read acyclically
Write parameter request: Reading the parameter value of r0002 from slave number 17
Value
11 h 1
10 h
0258 h
0007 h
0E h
0001 h
2F0A h
8001 h
0101 h
1001 h
0002 h
0000 h
xx h
xx h
182
Byte Description
Slave address
2 Function code (write multiple)
3,4 Register start address
5,6 Number of registers to be read (40601 ... 40607)
7 Number of data bytes (7 registers, each 2 bytes = 14 bytes)
8,9 40601: DS47 Control = 1 (activate request)
10,11 40602: Function 2F h (47), request length 10 bytes (0A h)
12,13 40603: Request reference = 80 h, request identifier = 1 h
14,15 40604: DO-Id = 1, number of parameters = 1
16,17 40605: Attribute, number of elements = 1
18,19 40606: Parameter number = 2
20,21 40607: Subindex = 0
22 CRC "Low"
23 CRC "High"
SINAMICS V20 Converter
Operating Instructions, 10/2019, A5E34559884-012