iSMA-B-MINI/MIX BACnet User Manual
www.ismacontrolli.com
DMP261en | 1st Issue rev. 8 | 05/2022
page 23 of 114
4.4 RS485 Port
4.4.1 RS485 Communication Bus Connection
Figure 25. RS485 connection
4.4.2 RS485 Network Termination
Transmission line effects often present problems 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.
4.5 Setting Module Address
4.5.1 Setting MAC Address in BACnet Protocol
The module is equipped with two rotary switches S1 and S2, located on the top panel of
the device, for determining the MAC address of the device.
It is possible to set the MAC address within the range from 0 to 99 in BACnet protocol
mode or from 128 to 227 in BACnet slave protocol mode (128 + switch value). The
formula for setting the MAC address is as follows:
MAC = S2
•
10 + S1
where S1 and S2 are the values of the switches.
The example of the
BACnet master protocol
mode:
