KP310V1.0 Controller Operation Manual
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13.3 Comm RTU
This communication protocol uses RTU (remote terminals communication unit ) mode, namely
binary.
Address field Function field Data field Data adjustment
field
Slave address Function code Data length Data CRC16
2Bytes 2Bytes 2Byte nBytes 2Bytes
13.3.1 Address field
Definition of address field is the only address in MODBUS.
This communication protocol applies to one-to-one communication between PC and controller.
Low byte is before the high byte.
13.3.2 Function field
Function code is the Host operation code and reply code from Host..
13.3.3 Data field
Value is the actual bytes of data (3.2)
Data type：2Byte
13.3.4 Data CRC field
Data check uses CRC16-CCITT as standard to check all data in MODBUS except data in check
field. Low byte stands after high byte.
The host machine sends messages to MODBUS and the slave produces CRC16 code to respond;
the host and slave have to calculate CRC16 code according to CRC16 multinomial.
CRC16-CCITT produces multinomial: X^16+X^12+X^5+1，CRC16-CCITT more details in
appendix 1 & 2.
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