Poseidon2
– Family manual
HW group
www.HW-group.com
89 / 104
Modbus over TCP
– Interface description
Modbus is a communication protocol designed for measuring devices that communicate over RS-485
or RS-232 (sometimes named Modbus RTU). The Modbus protocol itself allows to share the
memory area for variables
, e.g. the readings, over one of the physical interfaces. Modbus/TCP is
an extension of this protocol for communication over Ethernet.
Its advantages include easy implementation in industrial visualization systems. Current Modbus/TCP
description for Poseidon2 can be found on websites
http://new.hwg.cz/cs/node/4509
Mapping of variables for the Modbus/TCP protocol
Analog quantities
Address
I/O
Type Functions
Units
Description
100
Input
Int
4
Current number of installed (configured in
Setup) sensors
101-10x
Input
Int
4
0.1°C (K, F)
Current value of the sensor No. 1 through x,
where x is the value at address 100. Units are
configured in WEB Setup.
Binary values
Address
I/O
Type Functions
Units
Description
100 - 102
In
bit
2
0 / 1
Current values of binary inputs
200
In
bit
1
0 / 1
Reads the current value of the DTR output
200
Out
bit
5
0 / 1
Sets the value of the DTR output
201
In
bit
1
0 / 1
Reads the current value of the RTS output
201
Out
bit
5
0 / 1
Sets the value of the RTS output
The Poseidon2 works as a TCP Server at port 502 (Modbus standard). The Modbus/TCP
communication takes place using the given addresses. For details, see
http://www.modbus.org
.
Caution:
Modbus/TCP implementation support requires setting the "
Slave ID
" variable to number 2.
Check the setting of this variable in case you are enable to establish a connection. (The
actual name may differ in your software
– it used to be an address to distinguish
multiple devices on a RS-485 line in case of Modbus/RTU).
Note:
For details about Modbus/TCP, see on HWg websites
AN28: Damocles family &
Modbus/TCP
