4. Protocol description
PI130 series inverter communication protocol is a asynchronous serial master-slave
communication protocol, in the network, only one equipment (master) can build a
protocol (known as “Inquiry/Command”) . Other equipment (slave) only can response
the "Inquiry/Command"of master by providing data or perform the corresponding action
according to the "Inquiry/Command"of master. Here, the master refers to a Personnel
Computer (PC), an industrial control device or a programmable logic controller
(PLC),etc. and the slave refers to PI130 inverter. Master can communicate with
individual slave, also send broadcasting information to all the lower slaves. For the
single "Inquiry/Command"of master, slave will return a signal (that is a response) to
master; for the broadcasting information sent by master, slave does not need to feedback
a response to master.
5. Communication data structure
MODBUS protocol communication data format of PI130 series Inverter is divided
into RTU (remote terminal unit) mode
and ASCII (American Standard Code for Information International Interchange)
mode.
(1) In RTU mode, each byte format is as follows:
in RTU mode, messages are sent at a silent interval of at least 3.5 characters. There are
diverse character intervals under network baud rate,which is easiest implemented (as
shown in Figure T1-T2-T3-T4) . The first field transmitted is the device address. The
allowable characters for transmitting are hexadecimal 0 ... 9, A ... F. The networked
devices continuously monitor network bus, including during the silent intervals. When
the first field (the address field) is received, each device decodes it to find out if it is
sent to their own. Following the last transmitted character, a silent interval of at least 3.5
characters marks the end of the message. A new message can begin after this silent
interval. The entire message frame must be transmitted as a continuous stream. If a
silent interval of more than 1.5 characters occurs before completion of the frame, the
receiving device will flushes the incomplete message and assumes that the next byte
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