Command Code And Communication Data Illustration - Salicru CV30 User Manual

LRC CHK Lo
END Hi
END Lo
7.2.3.1 ASCII mode check (LRC Check)
Check code (LRC Check) is the value combined of address and data content result. For instance, the check code of
above 2.2.2 communication message is: 0x02+0x06+0x00+0x08+0x13+0x88=0xAB, then take the compliment of
2=0x55. Below is a simple LRC calculation function for user reference (programed with C language):
Static unsigned char
LRC(auchMsg,usDataLen)
unsigned char *auchMsg;
unsigned short usDataLen;
{
unsigned char uchLRC=0;
while(usDataLen--)
uchLRC+=*auchMsg++;
return((unsigned char)(~((char)uchLRC)));
}

7.3 Command code and communication data illustration

7.3.1 RTU mode
7.3.1.1 Command code: 03H
03H（correspond to binary 0000 0011）, read N words（Word）(the Max. continuous reading is 16 words)
Command code 03H means that if the master read data from the inverter, the reading number depends on
the "data number" in the command code. The Max. Continuous reading number is 16 and the parameter
address should be continuous. The byte length of every data is 2 (one word). The following command format
is illustrated by hex (a number with "H" means hex) and one hex occupies one byte.
The command code is used to read the working stage of the inverter.
For example, read continuous 2 data content from 0004H from the inverter with the address of 01H (read the
content of data address of 0004H and 0005H), the frame structure is as below:
RTU master command message (from the master to the inverter)
START
ADDR
CMD
High bit of the start address
Low bit of the start address
High bit of data number
Low bit of data number
CRC low bit
Communication protocol
8-bit check code is formed by the combination of two ASCII codes.
END Hi=CR (0x0D), END Lo=LF (0x0A)
End character:
T1-T2-T3-T4
01H
03H
00H
04H
00H
02H
85H
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