Siemens SINAMICS G120P, Руководство по эксплуатации

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Operation
6.8 Communication via RS485
Inverter cabinet units
Operating Instructions, 12/2014, A5E32923362A
237
6.8.3.4 Write and read access via FC 03 and FC 06
Function codes used
For data exchange between the master and slave, predefined function codes are used for
communication via Modbus.
The Control Unit uses the Modbus function code 03, FC 03 (read holding registers) for
reading, and the Modbus function code 06, FC 06 (preset single register) for writing.
Structure of a read request via Modbus function code 03 (FC 03)
Any valid register address is permitted as the start address.
The controller can use the FC 03 to access more than one register with one request. The
number of addressed registers is contained in bytes 4 and 5 of the read request.
Table 6- 22 Invalid read requests
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)
Table 6- 23 Structure of a read request for slave number 17
Example
Byte Description
11 h
03 h
00 h
6D h
00 h
02 h
xx h
xx h
0
1
2
3
4
5
6
7
Slave address
Function code
Register start address "High" (register 40110)
Register start address "Low"
Number of registers "High" (2 registers: 40110; 40111)
Number of registers "Low"
CRC "Low"
CRC "High"