INVT Goodrive350 Series Operation Manual page 317

Goodrive350 IP55 High-ingress Protection Series VFD
the each 8-bit character and the content in the register. The result is placed in the bits from the
least significant bit (LSB) to the most significant bit (MSB), and 0 is placed in the MSB. Then,
LSB is detected. If LSB is 1, the XOR operation is performed on the current value in the
register and the preset value. If LSB is 0, no operation is performed. This process is repeated
for 8 times. After the last bit (8th bit) is detected and processed, the XOR operation is
performed on the next 8-bit byte and the current content in the register. The final values in the
register are the CRC values obtained after operations are performed on all the bytes in the
frame.
The calculation adopts the international standard CRC check rule. You can refer to the related
standard CRC algorithm to compile the CRC calculation program as required.
The following example is a simple CRC calculation function for your reference (using the C
programming language):
unsigned
data_length)
{
int i;
unsigned int crc_value=0xffff;
while(data_length--)
{
crc_value^=*data_value++;
for(i=0;i<8;i++)
{
}
}
return(crc_value);
}
In the ladder logic, CKSM uses the table look-up method to calculate the CRC value according
to the content in the frame. The program of this method is simple, and the calculation is fast,
but the ROM space occupied is large. Use this program with caution in scenarios where there
are space occupation requirements on programs.
9.4 RTU command code and communication data
9.4.1 Command code 03H, reading N words (continuously up to 16 words)
The command code 03H is used by the master to read data from the VFD. The count of data to
be read depends on the "data count" in the command. A maximum of 16 pieces of data can be
int crc_cal_value(unsigned
if(crc_value&0x0001)
crc_value=(crc_value>>1)^0xa001;
else
crc_value=crc_value>>1;
char*data_value,unsigned
-299-
Communication protocol
char