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Modbus Considerations
The RS-485 interface suitable for Modbus
communication is 2-wire with shield non-isolated,
hence the following considerations apply:
• Maximum Modbus length ("L"):
4000 feet (1200 meters) for 9.6 – 78.8 kbps or
2600 feet (790 meters) for 115.2 kbps. It is
recommended that you select a low baud rate (for
example, 19.2 kbps) for reliable operation.
• Use only shielded, twisted pair of cables and daisy
chain topology.
• Ground noise should not exceed the EIA-485
common mode voltage limit.
HONEYWELL UNITARY CONTROLLER - 230 VAC - INSTALLATION INSTRUCTIONS
31
31-00610-01
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