Functions Codes; Modbus Commands - Siemens SITRANS F Operating Instructions Manual

Functions codes

6.1

Modbus Commands

Modbus addressing model
The module allows R/W access to the following standard Modbus data register blocks:
● Coils (ref. 0x address range)
● Holding Registers (ref. 4x address range)
I.e. the module will not support the other standard data register blocks:
● "Discrete Input" (ref. 1x address range)
● "Input Registers"(ref. 3x address range)
Commands
Broadcast communication from master to slave(s) through device address 0 is supported. No
response from the slave is generated in that case. Broadcast communication is not secured
by the normal check mechanisms and shall be limited to very few uses.
A SITRANS F Modbus slave only recognizes (and accepts) few Modbus RTU
commands/function codes.
Supported function codes are listed in the table below.
Table 6- 1 Function codes
Function code
01 hex
03 hex
05 hex
10 hex
11 hex
Modbus RTU RS485
Operating Instructions, 06/2010, A5E00753974-04
Command text
Read coils
Read multiple registers
Write single coil
Write multiple registers
Report Slave ID
Description
Reads the status of single bit(s) in a slave
Reads the binary content of multiple 16-bit registers in the slave.
The maximum number of registers is 26
Writes a single on/off bit
Preset values into a sequence of 16-bit registers. The maximum
number of registers is 25
The SITRANS F slave will respond to a Report Slave ID command
(Command 17) request from the master by giving in formation
about device type, vendor, revision level etc. in a format as shown
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