Rtu Command Code And Communication Data Illustration - IMO iDrive2 XKL Instruction Manual

iDrive2 inverters
{ 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.

7.3 RTU command code and communication data illustration

7.3.1 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 form 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 from0004H 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 bit
Low bit of the start bit
High bit of data number
Low bit of data number
CRC low bit
CRC high bit
END
T1-T2-T3-T4 between START and END is to provide at least the time of 3.5 bytes as the leisure time and
distinguish two messages for the avoidance of taking two messages as one message.
ADDR = 01H means the command message is sent to the inverter with the address of 01H and ADDR occupies
one byte
CMD=03H means the command message is sent to read data form the inverter and CMD occupies one byte
"Start address" means reading data form the address and it occupies 2 bytes with the fact that the high bit is in
the front and the low bit is in the behind.
"Data number" means the reading data number with the unit of word. If the "start address' is 0004H and the "data
number" is 0002H, the data of 0004H and 0005H will be read.
T1-T2-T3-T4 (transmission time of 3.5 bytes)
01H
03H
00H
04H
00H
02H
85H
CAH
T1-T2-T3-T4 (transmission time of 3.5 bytes)
75
Communication protocol