Janson Controls FC100 Series, Manual, Page: 96 / 108

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LRC Check is the value added from Address to Data Content . For example , the
LRC Check of the above 3 . 3 . 1 enquiry message is as : 01H + 03H + 21H + 02H +
00H + 02H = 29H , then the complement of2 ( D7H ) is taken .
CRC Check of RTU mode
CRC Check is from Address to Data content
, and its running rule is as follows :
Step 1 : Make 16 - bit temporary storage ( CRC temporary storage )= FFFFH .
Step 2 : Exclusive OR first 8 - bit byte message instruction and low 16 - bit CRC
temporary storage : Perform Exclusive OR , and store the result into CRC
temporary storage .
Step3 : Move CRC temporary storage one more bit , and fill 0 into high bit
position .
Step 4 : Check right shift value , if being 0 , store the new value for step 3 into
CRC temporary storage , otherwise in case of Exclusive OR A001H and CRC
temporary storage , store the result into CRC temporary .
Step 5 : Repeat Step 3 ~ Step 4 , and operate completely for 8 - bit . Step
6 : Repeat Step 2 ~ Step 5 , and take the message instruction for next 8 - bit , till all
message instructions are operated completely .
Finally , the value gotten of CRC temporary storage is CRC Check . It is
noteworthy that , CRC Check must be placed into the check mode of message
instruction interchangeably .
The following is the example of CRC Check running written in C language :
Unsigned char * data —// Message instruction pointer Unsigned char length
<—// Length of message instruction unsigned int crc _ chk ( unsigned char * data ,
unsigned char length )
6
Chapter 6 Description of parameter setting
FC100 Series User Manaul