Appendix I
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There are diverse character intervals under network baud rate,
which is easiest implemented. 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.
RTUframe format :
Frame header START
Time interval of 3.5characters
Slave address ADR
Communication address: 1 to 247
Command code CMD
03: read slave parameters
；
06: write slave parameters
Data content DATA(N-1)
Data content: address of function code parameter, numbers of
function code parameter, value of function code parameter, etc.
Data content DATA(N-2)
………………………
Data content DATA0
CRC CHK high-order
Detection Value: CRC value.
CRC CHK low-order
END
Time interval of 3.5characters
CMD (Command) and DATA (data word description)
Command code: 03H, reads N words (max.12 words), for example: for the inverter with slave
address 01, its start address F0.02 continuously reads two values.
Master command information
ADR
01H
CMD
03H
Start address high-order
F0H
Start address low-order
02H
Number of registers high-order
00H
Number of registers low-order
02H
CRC CHK low-order
CRC CHK values are to be calculated
CRC CHK high-order
Slave responding information
When F9.05 is set to 0:
ADR
01H
CMD
03H
Byte number high-order
00H
Byte number low-order
04H
Data F002H high-order
00H
Data F002H low-order
01H
Data F003H high-order
00H
Data F003H low-order
01H
CRC CHK low-order
CRC CHK values are to be calculated
CRC CHK high-order
When F9.05is set to 1:
ADR
01H
