Write And Read Access Using Function Codes - Siemens SINAMICS S120 Function Manual

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Communication

11.4 Communication via MODBUS TCP

Write and read access using function codes

Function codes used

For data exchange between the controller and device, predefined function codes are used

for communication via Modbus.

The Control Unit uses the following Modbus function codes:

● FC 03: Holding register to read data from the inverter

● FC 06: Write single register to write to individual register

● FC 16: Write to multiple registers to write to several registers

Structure of a Modbus TCP message

Figure 11-50 Individual components, including Modbus Application Header (MBAP) and function code

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 11- 22 Structure of a read request for device number 17, example

Number of registers "High" (2 registers: 40110; 40111)

number of registers "Low"

Function Manual, 11/2017, 6SL3097-4AB00-0BP5

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