Chapter 7 Modbus Communication Protocol
ACH200 Series High Voltage Variable Frequency Speed Control System Operating Manual
66
7.2.1 Slave Address
Please set the value of 0~247 (Decimal). When the slave address is set to 0, the host sends in a
broadcast mode, and all slaves receive instructions.
For broadcast transmission, the slave station does not send response information to the master
station.
7.2.2 Command Code
Command Code
Function
03H
Read slave parameters
06H
Write slave parameters
7.2.3 Data
The number of the AC drive parameter code and the data corresponding to the parameter code
are combined into a series of data, including reading the data of the parameter code or a specific
address, writing data to the parameter code or a specific address, etc.
7.2.4 Check
The standard Modbus communication uses two error detection methods, where parity is used
to check each character and CRC detection is used to check a frame of data.
1. Parity check
The user can configure the controller to be odd or even parity, or no parity. This will determine
how the odd or even parity bits are set in each character.
If odd or even parity is specified, the number of "1" bits will count towards the number of bits
in each character (7 data bits in ASCII mode, 8 data bits in RTU). For example, the RTU character
frame contains the following 8 data bits: 1 1 0 0 0 1 0 1, the whole number of "1's" is 4.
If even parity is used, the parity bit of the frame will be 0, so the whole number of "1's" will
still be 4. If odd parity is used, the parity bit of the frame will be 1, and the number of "1s" will be
5.
If no parity bit is specified, no parity bit is transmitted, and no parity detection is performed.
Instead of the additional stop bits, they are filled in the character frame to be transmitted.
2. CRC-16 (Cyclic Redundancy Check)
