Siemens sinamics dcp - Page 283

Operation
7.7 Communication via Modbus TCP
SINAMICS DCP
Operating Instructions, 09/2019, A5E34382853K
281
Structure of a read request via Modbus function code 03 (FC 03)
Any valid register address is permitted as the start address.
Via FC 03, the control can address more than one register with one request. The number of
addressed registers is contained in bytes 10 and 11 of the read request.
Table 7- 35 Structure of a read request for device number 17, example
Value
Byte
Description
MBAP header
03 h
00 h
6D h
00 h
02 h
7
8
9
10
11
Register start address "High" (register 40110)
Register start address "Low"
Number of registers "High" (2 registers: 40110; 40111)
number of registers "Low"
The response returns the corresponding data set:
Table 7- 36 Device response to the read request, example
Value
Byte
Description
MBAP header
03 h
04 h
11 h
22 h
33 h
44 h
7
8
9
10
11
12
Function code
Number of bytes (4 bytes are returned)
Data, first register "High"
Data, first register "Low"
Data, second register "High"
Data, second register "Low"
Table 7- 37 Invalid read request
Read request
Inverter response
Invalid register address
Exception code 02 (invalid data address)
Read a write-only register
Telegram in which all values are set to 0.
Read a reserved register
Controller addresses more than 125 registers
Exception code 03 (invalid data value)
The start address and the number of registers of an
address are located outside of a defined register
block
Exception code 02 (invalid data address)