Function code Command text Description
03 Read Holding Registers Reads the binary content of multiple 16-bit registers
04 Read Input Registers Reads the binary content of multiple 16-bit registers
05 Write Single Coil Writes a single on/off bit
06 Write Single Register Writes the binary content of single 16-bit register
07 Read Exception Status Delivers the global alarm status of the device
08 Diagnostics Provides a series of tests for checking the communication sys‐
tem
15 Write Multiple Coils Writes multiple on/off bits
16 Write Multiple Registers Writes the binary content of multiple 16-bit registers
17 Report Slave ID The device will respond to a Report Slave ID command (com‐
mand 17) request from the master by giving information about
device type, vendor, and revision level
23 Read/Write Multiple Registers Combined Write Multiple Registers / Read Holding Registers call
Function code 7 (Read exception status)
The device provides the content of the parameter Global alarm status as exceptions.
Function code 8 (Diagnostics)
The diagnostics function provides means for checking the communication between MODBUS
master and slave. The function uses a sub-function code to select the functionality.
The following sub-function codes are supported:
Sub-function code Name Description
0 Return query data The data passed in the request data field will be returned (loo‐
ped back) in the response. The entire response message should
be identical to the request.
1 Restart communications option After having restarted the communication, select the baudrate,
framing or Modbus address to get access to the device again.
Function code 17 (Report Slave ID)
The transmitter will respond to a Report Slave ID request from the master by giving information
about device type, vendor, and firmware version in a format as shown:
Response
Slave address 1 byte
Function code 1 byte 17
Byte count 1 byte 62
Slave ID 1 byte Sensor device type
0: SITRANS FS
Run indicator 1 byte 255: Running
Manufacturer name 12 bytes SIEMENS
Product name 32 bytes SITRANS F
Product firmware
version
16 bytes -
CRC 2 bytes
Modbus communication
A.7 Modbus function codes
SITRANS FST030 (Modbus)
Operating Instructions, 08/2018, A5E37367739-AD 139
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