Function Code 02 (Read Input Status); Function Code 05 (Force Single Coil); Function Code 03 (Read Holding Register) - Samson Trovis 6400 Mounting And Operating Instructions

Interface RS-485

9.5.2. Function code 02 (Read Input Status)

This function code allows to read the current status of the binary inputs bi 1, bi 2 and bi 3
directly at the input of the slave, no matter whether the respective binary input was configured
in the process control station.
For the query from the central control station and the response from the process control station,
see Read Coil Status (Function code 01).

9.5.3. Function code 05 (Force Single Coil)

The central control station can modify a logic condition in the process control station.
Example: Write coil 09 (MANUAL/AUTOMATIC changeover).
coil 09 must set to "0" in order to place the process control station in the AUTOMATIC mode.
In this example, the address of the process control station is 12.
Query from the control station
Address Function
0C 05
Response from the process control station
Address Function
0C 05
The fourth byte contains number 9 (hexadecimal). If a coil is set to "1", byte 5 must transmit the
information FF. If it is to be deleted, 00 has to be transmitted.

9.5.4. Function code 03 (Read Holding Register)

Analog variables can be read from the process control station and, after conversion to the
numeric format, displayed on the PC (controlled variable, set point (reference variable) etc.),.
Example: Read holding register no. 1
This register contains the device identification. The address of the process control station is 1.
Query from the control station
Address Function
01 03
Response from process control station
Address Function
01 03
Since, in this example, only register 1 is read and this register always contains the decimal
value 6412, it can be used to check the device identification.
Coil
high low
00 09
Coil
high low
00 09
Holding register no.
high low
00 00
Quantity of Value of register 1
bytes
high
02 19
Functions supported by the Modbus protocol
Coil
on off
FF 00
Coil
on/off
FF 00
Quant. of holding registers
high low
00 01
low
0C
Checksum
low high
5D 25
Checksum
low high
5D 25
Checksum
low high
84 0A
Checksum
low high
B3 D1
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