Powtran PI500-W 004G1, Manual

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Appendix I
72
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I
CRC CHK low-order
CRC CHK values are to be calculated
CRC CHK high-order
Command Code: 06H, write a word. For example: Write 5000(1388H)into the address F013H
of the inverter with slave address 02H.
Master command information
ADR 02H
CMD 06H
Data address high-order F0H
Data address low-order 13H
Data content high-order 13H
Data content low-order 88H
CRC CHK low-order
CRC CHK values are to be calculated
CRC CHK high-order
Slave responding information
ADR 02H
CMD 06H
Data address high-order F0H
Data address low-order 13H
Data content high-order 13H
Data content low-order 88H
CRC CHK low-order
CRC CHK values are to be calculated
CRC CHK high-order
I-2 Check mode:
Check mode - CRC mode: CRC (Cyclical Redundancy Check) adopts RTU frame format, the
Message includes an error-checking field that is based on CRC method. The CRC field checks
the whole content of message. The CRC field has two bytes containing a 16-bit binary value. The
CRC value calculated by the transmitting device will be added into to the message. The receiving
device recalculates the value of the received CRC, and compares the calculated value to the Actual
value of the received CRC field, if the two values are not equal, then there is an error in the
transmission.
The CRC firstly stores 0xffff and then calls for a process to deal with the successive eight-bit
Bytes in message and the value of the current register. Only the 8-bit data in each character is
valid to the CRC, the start bit and stop bit, and parity bit are invalid.
During generation of the CRC, each eight-bit character is exclusive OR(XOR) with the
register
Contents separately, the result moves to the direction of least significant bit(LSB), and the
most significant bit(MSB) is filled with 0. LSB will be picked up for detection, if LSB is 1, the
register will be XOR with the preset value separately, if LSB is 0, then no XOR takes place. The
whole process is repeated eight times. After the last bit (eighth) is completed, the next eight-bit
byte will be XOR with the register's current value separately again. The final value of the register
is the CRC value that all
The bytes of the message have been applied.
When the CRC is appended to the message, the low byte is appended firstly, followed by the
high byte. CRC simple functions is as follows:
Unsigned int crc_chk_value(unsigned char *data_value,unsigned char length)
{
unsigned int crc_value=0xFFFF;
int i;
while(length--)
{
crc_value^=*dat+;