Rtu Command Code And Communication Data Illustration; Rtu Mode - INVT Goodrive200A Series Operation Manual

GD200A series VFD
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 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.

9.4 RTU command code and communication data illustration

9.4.1 RTU mode

9.4.1.1 Command code: 03H
read N words (Word) (N≤16)
Command code 03H means that if the master read data from the VFD, the reading number depends
on the "data number" in the command code. 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 step of the VFD.
For example, read continuous 2 data content from0004H from the VFD 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 VFD)
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
CRC high bit
END
}
T1-T2-T3-T4 (transmission time of 3.5 bytes)
T1-T2-T3-T4 (transmission time of 3.5 bytes)
-131-
Communication protocol
01H
03H
00H
04H
00H
02H
85H
CAH