ABB Arc Guard System TVOC-2-COM, Configuration Manual

Page: 13 / 40

ABB ARC GUARD SYSTEM™ – TVOC-2-COM MODBUS CONFIGUR ATION MANUAL 13
2.4 Termination
For best quality of data transfer, Modbus should be
terminated correctly.
The following figure shows Modbus installation according
to [3].
2.4.1 Termination resistors
A 120Ω resistor is added in parallel with TVOC-2 System
connection if it is installed as first or last device on the
network. For this purpose there are double terminals for
+(B) and -(A) connections.
2.4.2 Pull-up / pull-down resistors
When the Modbus network is not being actively driven
by a device, the bus line is in an undefined state. Bias
resistors should then be used to obtain a defined voltage
potential on the data lines. The bias resistors act for data
line B (D1) as pull-up resistors against 5V and for data
line A (D0) as pull-down resistors against GND. This is
illustrated in Figure 20 in [2].
The following devices usually have built-in bias resistors:
• Modbus masters
• Gateways
• Repeaters
Figure 3
General 2-Wire Topology
02
Draft, ne pas diffuser Wed Dec 05 2018 12:41:51 GMT+0100 (Romance Standard Time)