9. Peripherals and Options MD500 User Manual
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Terminal Wiring
1. Terminal wiring if the node has the CGND terminal
The MD38TX1 has three cables to connect the 485+, 485- and CGND terminals respectively. Check that the RS485 bus on site
has these three cables and the terminals are not connected reversely or wroingly.
If a shielded cable is used, the shield must also be connected to the CGND terminal. Except this CGND terminal, prevent the
shield from touching anywhere of the drive including the drive housing and the grounding terminal of the equipment.
Due to cable attenuation, if the connection length is larger than 3 m, use the AGW26 or a thicker cable. Always use a twisted
pair cable to connect 485+ and 485- respectively.
Non-shielded multi-core twisted pair cable and STP cable are recommended. If non-shielded multi-core twisted pair cable is
used, take the twisted pair to connect 485+ and 485- and twist the other unused cables into one rope and connect it to CGND.
If an STP cable is used, connect the twisted pair to 485+ and 485- respectively and the shield to CGND. The shield can be
connected to CGND only. It must not be connected to ground.
485
node
485+
485-
CGND
485
node
485+
485-
CGND
Non-shielded multi-
core twisted pair
cable
STP cable
2. Terminal wiring if the node does not have the CGND terminal
For the nodes without the CGND terminal, never connect the CGND cable or the shield to the PE of the node directly.
485
node
485+
485-
485
node
485+
485-
Shield unconnected
CGND cable unconnected
Take the following steps to handle it.
Step 1: Check whether a common reference ground of the 485 circuit exists on other ports of this node. If yes, connect the
CGND cable or the shield to the pin.
Step 2: Check whether the reference ground of the 485 circuit exists on the board of the node. If yes, connect the CGND cable
or the shield to it.
Step 3: If the reference ground of the 485 circuit is not found, keep the CGND cable or the shield unconnected and use an
extra ground cable to connect this node to the PE of other nodes.
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Transmission Distance
The maximum number of nodes and transmission distance of the standard RS485 circuit vary with different baud rates, as listed in
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No. Baud Rate Max. Transmission Distance Number of Nodes Cable Diameter
1 115.2 Kbps 100 m 128 AWG26
2 .ESV 1000 m 128 AWG26
For details of the Modbus communication protocol, see section 8.5 Modbus Communication Protocol.
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