Modbus RTU rules
The RS-232 port supports the connection of one Modbus RTU (RS-232) device. With the addition
of an RS-232/RS-485 converter and connection to the RS-232 port, up to 32 Modbus RTU (RS-485)
devices are supported. Observe the rules in the following table when designing and installing the
connected Modbus RTU Bus.
Table 6: Modbus RTU rules table
Category Rules/maximums allowed
General Supports one direct Modbus RTU (RS-232) connection to the RS232C port.
A connection of an RS-232/RS-485 converter to the RS232C port supports
up to 32 Modbus (RS-485) devices.
FC port does not support Modbus integration.
Number of Devices RS232C port supports one Modbus RTU (RS-232) device.
RS232C port with RS-232/RS-485 converter supports up to 32 Modbus
(RS-485) devices.
Cable Length RS-232 cable length can be up to 15 m (49.2 ft).
RS-485 cable length can be up to 1,520 m (4,987 ft).
Cable RS-232 stranded cable, 3-9 conductors, serial data grade, 20–24 AWG.
RS-485 stranded cable, 0.6 mm (22 AWG) 3-wire twisted, shielded cable is
recommended. Stranded 0.6 (22 AWG) 4-wire (two twisted pairs) shielded
is acceptable.
EOL Termination RS-232: requires no termination.
RS-485: End-of-line (EOL) termination must be set to On (or an EOL
terminator installed) on the two devices located at either end of each
bus segment on an RS-485 bus. The EOL switches must be set to Off (or
EOL termination disabled) for all other devices on the bus segment on an
RS-485 bus.
11NCE25 Installation Instructions
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