TP Software User Manual
www.ismacontrolli.com
DMP253en | 1st Issue rev. 0 | 04/2022
page 5 of 49
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2 Communication Protocols
The TP panel supports Modbus RTU/ASCII and BACnet MS/TP communication protocols,
using 2 RJ45 sockets and a screw terminal (one RS485 port).
Note:
A communication protocol is selected by setting a second switch on the DIP switch
on the back of the panel:
Off:
Modbus RTU/ASCII (default);
On:
BACnet MS/TP.
The Modbus address of a server device is set using the rotary switch.
Note:
If the rotary switch is set to 0, the address is read from the ADDRESS register/object
(decimal address: 22). See
Other communication parameters such as baud rate, number of data/stop bits, or parity
bit are set using relevant Modbus registers or BACnet objects.
2.1 RS485 Connection
Figure 1. RS485 communication diagram
2.2 RS485 Network Termination
Transmission line effects often present a problem for data communication networks.
These problems include reflections and signal attenuation. To eliminate the presence of
reflections of signal from the end of the cable, the cable must be terminated at both ends
with a resistor across the line adequate to its characteristic impedance. Both ends must
be terminated since the propagation is bidirectional. In case of an RS485 twisted pair
cable this termination is typically 120
Ω.
Note:
A termination resistor can be added with a third switch on the DIP switch on the
back of the panel:
off:
termination resistor disconnected (default);
on:
termination resistor added.
