Communication Frame Structure - Veichi Electric AC60 series Manual

5.1 Communication frame structure

The ModBus protocol communication data format of the AC60 series frequency
inverter is RTU (long-range terminal unit) mode, communication data format is
as follows:
The byte composition: Include initiation bit, 8 data bit, check bit and
stop bit.
Sta
rt Bit1 Bit2 Bit3
bit
In RTU mode, it always begins with transmission time pause gap of at least
3.5 bytes. With various character and time under the Baud rate, it is very
easy to realize the transmission time of 3.5 bytes. The successive order of
the following transmission data domains: slave machine address、operation
command code、data and CRC checking bit. Transmission byte of each domain is
sexadecimal 0...9，A...F. Network equipment detects the network network bus
unceasingly, including the pause gap time. While receiving the first domain
(address information), each network equipment carries out decoding to judge
whether the byte is sent to it. While the final byte transmission is completed,
there will be an at least 3.5 bytes transmission time pause gap to indicate
that this frame is over. Then a new information' transmission can begin.
There is at lowest
slave machine
3.5 bytes vacancy at
address
beginning
Bit4 Bit5 Bit6
RTU DATA FRAME FORMAT
MODBUS MESSAGE
function
data
code
176
No check
bit
Even check
Bit7 Bit8
bit
Odd check
bit
There is at lowest
checking
3.5 bytes vacancy at
ending