Unitronics UMI-B1 UL Series Operation Manual page 116

UMI-B1 UL Series Inverter
the receiving data is different from the setting value, there is an error in the
communication.
CRC check
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 x 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 x data_value,unsigned char data_length)
{
int i;
unsigned int crc_value=0xffff;
while(data_length--)
{ crc_value^= x 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 easy program and quick calculation speed. But the
ROM space the program occupied is huge. So use it with caution according to the
program required space.
}
114
Communication protocol