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8. At the MP2, connect the cable shield to the protective (protected) earth ground. The cable
shields must not be connected to earth ground anywhere else in the cabling network except at
this point.
3.5 Line Termination
1. At each end of the Modbus cable network daisy-chain, there must be an end of line termination
resistor. Connect a 1/2W 120-ohm resistor across the D0 and D1 conductors of the end devices.
2. If the MP2x is at one end of the Modbus cable network, then use the built in End of Line resistor.
Remove the cover of the MP2x and locate DIP switch in the front right corner of the board. SW3
is for COM1. Press switch number 2 down (middle switch) to enable the end of line terminating
resistor. If the MP2x is not the last device on the Modbus cable network, then move switch 2 to
the up position. No more than two-line terminations are allowed per Modbus cable network.
3.6 Line Polarization
When there is no data activity on an RS-485 balanced pair, the lines are not driven and, thus susceptible
to external noise or interference. To ensure the receiver line stays in a constant state, when no data
signal is present, some devices need to bias the network. Polarization of the pair must be implemented
at one location for the entire Serial Bus. Generally this is at the primary device such as the MP2. Other
devices must not implement any polarization. Refer to the manual of the device you are monitoring to
determine if line biasing is required.
Line polarization should be accomplished (if needed) from the Primary polling device. Leave switches 1
& 3 in the up position on the MP2x. Refer to Figure 7.
Rev 2.1 10/21/21
Ground Shield at MP2
ground post
Figure 6 - Modbus Wiring MP2 to MP2x
COM 1
Figure 7 - Modbus End of Line and Line Polarization Jumpers
- 7 -
©
TELSEC
MP2X User Guide
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