master only by providing the data or doing the action according to the master’s
“Inquiry/Command”. Here, master is Personnel Computer, Industrial Machine or
Programmable logical controller, and the slave is inverter. Master not only visits
some slave, but also sends the broadcast information to all the slaves. For the single
master “Inquiry/Command”, all of slaves will return a signal that is a response; for
the broadcast information provided by
master, slave needs not feedback a response to master machine.
8.5 Communication frame structure
ModBus protocol communication data format of C220/C420series of inverter is
shown as following: （In RTU mode, messages start with a interval of at least 3.5
character times. The first field then transmitted is the device address. The allowable
characters transmitted for all fields are
hexadecimal 0 ... 9, A ... F. Networked devices monitor the network bus continuously,
including during the silent intervals. When the first field (the address field) is
received, each device
decodes it to find out if it is the addressed device. Following the last transmitted
character, a
similar interval of at least 3.5 character times marks the end of the message. A new
message can begin after this interval).
The entire message frame must be transmitted as a continuous stream. If a silent
interval of more than 1.5 character times occurs before completion of the frame, the
receiving device flushes the incomplete message and assumes that the next byte will
be the address field of a new message.
Similarly, if a new message begins earlier than 3.5-character times following a
previous message, the receiving device will consider it a continuation of the
previous message. This will set an
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