CRC is stored in 0xFFFF first , and then calls a process to compare the continuous 8 -bit bytes
in the message with the value in the current register line processing. Only the 8Bit data in each
character is valid for CRC , and the start and stop bits and parity bits are all invalid.
CRC generation, each 8 -bit character is individually exclusive or ( XOR ) with the contents of
the register, and the result moves towards the least significant bit, and the most significant bit is filled
with 0 . The LSB is extracted and detected. If the LSB is 1 , the register is exclusive or different from
the preset value. If the LSB is 0 , it will not be performed. The whole process is repeated 8 times.
After the last bit ( bit 8 ) is complete, the next
Each 8 -bit byte is individually exclusive-ored with the current value of the register. The value in
the final register is the CRC value after all bytes in the message have been executed .
CRC is added to the message, the low byte is added first, followed by the high byte. The simple
function of CRC is as follows:
‹
Function code parameter address marking rules:
Read and write function code parameters (some function codes cannot be changed and are
only used by the manufacturer or monitored):
Use the function code group number and label as the parameter address to express the rules:
High byte: P0~PF ( Group P ), A0~AF ( Group A ), 70~7F ( Group U )
Low byte: 00~FF
For example: if you want to range function code P3-12 , then the access address of the function
code is expressed as F30C H
Notice:
PF group: parameters cannot be read or changed;
A
Janson Controls Technologies(Shenzhen) Co.,Limited
Appendix A MODBUS Communication Protocol
FC100P Series Manual V1.0
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