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RS-485 two-wire wiring method is half-duplex serial communication. At the same
moment the host and slave can not simultaneously transmit or receive data. Only one
transmits data and another receives them.
RS-485 two-wire wiring method supports bus-type topological structure. At most 31
nodes can be connected to the same bus. Normally master-slave communication
method is adopted in the RS-485 communication network, namely, one master
commands as many as 31 slaves.
Under the circumstance of multi-computer communication or long-distance
communication, it is suggested to connect the signal ground of the master station with
the common port of the inverter to raise the ant-interference ability of communication.
A2．Modbus protocol
Modbus is a master-slave communication protocol. The master governs the whole
communication process. Only when the master sends command to the slave, the slave
executes the actions or/and send feedback information to the master. Otherwise the
slave performs no operation and the slave can not communicate with each other directly.
There are two kinds of dialog between the master and slaves:
(1) Point-to-point: Master sends command individually to a certain slave which executes
action or/and sends feedback information.
When the master command is correct, the slave executes corresponding actions and
transmits feedback of result information to the master.
When the master command is false, the slave transmits feedback of error information to
the master but executes no actions.
(2) Broadcast mode: The master sends command to all slaves which execute action but
send no feedback information.
Modbus protocol has two kinds of transmission patterns: Modbus RTU and Modbus
ASCII. QD series frequency inverter supports Modbus RTU.
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General