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Revision 4
Markings that indicate polarity on the RS-485-to-USB converter supplied by Sintrol are
inverted. When using RS-485-to-USB converter supplied by Sintrol, connect wire A to +
and wire B to −.
Some manufacturers have the RS-485 output signals inverted, and the way signal polarity is labeled can
differ between manufacturers. For example, some manufacturers indicate negative polarity with
TX−/RX− or D− instead of A, and positive polarity with TX+/RX+ or D+ instead of B.
If you are connecting the device into an existing Modbus RTU automation system or if
you are using a third-party RS-485-to-USB converter or cable, read the related user
documentation carefully before connecting the RS-485 output.
Connecting RS-485 bus
Figure 24: Modbus RTU bus on the main board
Connect the sheath of a shielded cable to ground only on one end. Connecting both
ends to ground can create a ground loop.
To connect a RS-485 bus, you need:
Protective gear for electric work
Pin wrench or
1
⁄
2
-inch ratcheting socket wrench
Slotted-head screwdriver (M3)
Wrench (20 mm [0.7874 in] or adjustable)
Suitable signal cable
A
G
B
Modbus RTU
master or
Sintrol router
Next device in
the network
