9.8 Wiring Instructions
9.8.1 Topology
No repeater RS-485-Modbus has a trunk cable to which all devices are connected directly (daisy-type) or
via short branch cables.
The trunk cable, also known as the bus, can be very long. It must be terminated at both ends. It is also
possible to use a repeater between multiple RS-485 Modbus . And the address of each slave address in the
network is unique, which is the basis for ensuring Modbus serial communication.
9.8.2 Length
The end-to-end length of trunk cables must be limited. The maximum length is related to baud rate, cable
(gauge, capacitance or characteristic impedance), number of loads on the daisy chain, and network configuration
( 2- wire or 4 -wire).
For cables with a high-speed baud rate of 9600bps and AWG26 (or thicker) specifications, the maximum
length is 1000m .
Branches must be short and cannot exceed 20m . If a multi-port splitter with n branches is used, the
maximum length of each branch must be limited to 40m divided by n .
9.8.3 Grounding form
" common " circuit (signal and optional power common) must be connected directly to protective ground,
preferably at a single point along the entire bus. Typically, this point can be selected on the master or its taps.
9.8.4 Cable
Modbus cable on the serial link must be shielded. At one end of each cable, its shield must be connected
to protective earth. If a connector is used at this end, connect the connector housing to the cable shield. RS485
-Modbus must use a balanced pair and a third wire (for common) .
For RS485-Modbus , the cable diameter must be chosen wide enough to allow the use of the maximum
length ( 1000m ). AWG24 can meet the needs of Modbus data transmission.
9.9 Communication exception code definition
When the corresponding error information is detected during the communication process, the lower
computer (that is, the CPU board) will set the high position of the function code to "1" and feed back the
corresponding error code (abnormal code), so that the upper computer can identify the cause of the current
error and respond accordingly The definition is shown in Table 9.6 .
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NVF2G Series Inverter User's Guide
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