INVT 11020-00136, Operation Manual

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Goodrive600 series high-performance multifunction VFD Communication networking
-119-
reflection.
Rectifier unit Inverter unit 1 Inverter unit 2 Inverter unit N
485+
485-
485+
485-
485+
485-
485+
485-
...
PLC
A B A B A B A B
RS485
Figure 6-1 Network topology
6.3.2 RTU mode
6.3.2.1 RTU communication frame structure
When a controller is set to use the RTU communication mode on a Modbus network, every byte (8 bits) in the message
includes 2 hexadecimal characters (each includes 4 bits). Compared with the ASCII mode, the RTU mode can help to
send more data at the same baud rate.
Code system

1 start bit

7 or 8 data bits; the minimum valid bit is sent first. Each frame domain of 8 bits includes 2 hexadecimal characters (0
–
9, A
–F).

1 odd/even check bit; this bit is not provided if no check is needed.

1 stop bit (with check performed), or 2 bits (without check)
Error detection domain

Cyclic redundancy check (CRC)
The following table describes the data format.
11-bit character frame (Bits 1 to 8 are data bits):
Start bit BIT1 BIT2 BIT3 BIT4 BIT5 BIT6 BIT7 BIT8 Parity bit Stop bits
10-bit character frame (Bits 1 to 7 are data bits):
Start bit BIT1 BIT2 BIT3 BIT4 BIT5 BIT6 BIT7 Parity bit Stop bits
In a character frame, only the data bits carry information. The start bit, check bit, and stop bit are used to facilitate the
transmission of the data bits to the destination device. In practical applications, you must set the data bits, parity check
bits, and stop bits consistently.
In RTU mode, a new frame always must be preceded by a time gap with a minimum length of 3.5 bytes. On a network
where the transmission rate is calculated based on the baud rate, the transmission time of 3.5 bytes can be easily
obtained. After the idle time ends, the data domains are sent in the following sequence: slave address, operation
command code, data, and CRC check character. Each byte sent in each domain includes hexadecimal characters (0
–9,
A
–F). The network devices always monitor the communication bus. After receiving the first domain (address information),