Goodrive300-01A series VFD for air compressor
Communication protocol
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Appendix D Communication protocol
D.1 Application mode
The Modbus protocol of this VFD is RTU mode and the network line is RS485.
The interface of RS485 works on semiduplex and its data signal adopts differential transmission
mode which is also called balance transmission, too. It uses twisted pairs, one of which is defined as
A (+) and the other is defined as B (-). Generally, if the positive electrical level sending between drive
A and B is among +2 to +6V, it is logic
“1”, if the electrical level is among -2V to -6V; it is logic “0”.
485+ on the VFD terminal board corresponds to A and 485- to B.
Communication baud rate (P14.01) means the binary bit number transmitted in one second. The unit
is bit/s (bps). The higher the baud rate is, the quicker the transmission speed is and the weaker the
anti-interference is. If the twisted pairs of 0.56mm (24AWG) is used as the communication cables, the
max. transmission distance is as below.
Baud rate (bps)
Max. transmission
distance
Baud rate
(bps)
Max. transmission
distance
2400
1800m
9600
800m
4800
1200m
19200
600m
It is recommended to use shield cables and make the shield layer as the grounding lines during
RS485 remote communication.
In the cases with less devices and shorter distance, it is recommended to use 120Ω terminal resistor
as the performance will be weakened if the distance increases even though the network can perform
well without load resistor.
D.2 RTU command code and communication data
Command code: 03H, read N words (N≤16)
Command code 03H means that if the master read data from the VFD, the data number depends on
the “data number” in the command code. The max. number is 16 and the parameter address to be
read must be continuous. The length of every data is 2 bytes (one word). The following command
format is illustrated in hex (a number with “H” means hex) and one hex number occupies one byte.
This command code is used to read the parameter and working state of the VFD.
Command code: 06H, write one word
This command means the master writes data to the VFD and one command can write one data only.
It is used to change the parameter and working mode of the VFD.
Command code: 08H, diagnosis function
Meaning of sub-function codes:
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