Powtran PI9000 series, Быстрое руководство, Страница: 47 / 52

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Communication data structure PI9000 series inverter's Modbus protocol
communication data 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 will be the address field of a new message.
Similarly, if a new message begins earlier than the interval of 3.5 characters
following a previous message, the receiving device will consider it as a
continuation of the previous message. This will result in an error, because
the value in the final CRC field is not right.