SD1 Series Inverters Communication Protocol
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is applied, the even check bit is "1"; if the odd checkout is applied; the odd check bit is "0". The
even and odd check bit is calculated on the check bit position of the frame. And the receiving
devices also carry out even and odd checkout. If the parity of the receiving data is different
from the setting value, there is an error in the communication.
Cyclical Redundancy Check (CRC) method
The checkout uses RTU frame format. The frame includes the frame error detection field
which is based on the CRC calculation method. The CRC field is two bytes, including 16 figure
binary values. It is added into the frame after calculated by transmitting device. The receiving
device recalculates the CRC of the received frame and compares them with the value in the
received CRC field. If the two CRC values are different, there is an error in the communication.
During CRC, 0*FFFF will be stored. And then, deal with the continuous 6-above bytes in the
frame and the value in the register. Only the 8Bit data in every character is effective to CRC,
while the start bit, the end and the odd and even check bit is ineffective.
The calculation of CRC applies the international standard CRC checkout principles. When the
user is editing CRC calculation, he can refer to the relative standard CRC calculation to write
the required CRC calculation program.
Here provided a simple function of CRC calculation for the reference (programmed with C
language):
unsigned int crc_cal_value(unsigned char *data_value,unsigned char
data_length)
{
int i;
unsigned int crc_value=0xffff;
while(data_length--)
{ crc_value^=*data_value++;
for(i=0;i<8;i++)
{
if(crc_value&0x0001)crc_value=(crc_value>>1)^0xa001;
else crc_value=crc_value>>1;
} }
return(crc_value);
}
In ladder logic, CKSM calculated the CRC value according to the frame with the table inquiry.
The method is advanced with an easy program and quick calculation speed. But the memory
space the program occupies is huge. So, use it with caution according to the program space
available.
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