Alpha 6000S series User Manual page 203

Appendix 4 Use of MODBUS Communication
 Command Formatting
During communication, the main controller (PLC, etc) gives commands to ALPHA6000S/ALPHA6000V,
and the frequency inverters respond to them. The process constitutes the information transmission &
receiving as showed in the right figure. As the command function content varies, the length of data will vary
as well. The interval between two commands should maintain the time recorded below.
PLC
Command
指令
3.5char
Frequency inverter address: Frequency inverter address (0 ~ 31)
When it is set as 0, commands are transmitted together with the broadcast manner. Even if the broadcast command is
received, the frequency inverter will not give response.
 Command Code
There are four types of MODBUS command codes supported by the series of frequency inverters, which are
showed as follows:
Command
Code Function
(16 bits )
03H Reading Record
Single Character
06H
Writing
08H Loopback Test
10H Writing Record

CRC Check
The calculation method for CRC-16 used by MODBUS communication is as follows:
1. Generally, when CRC-16 is calculated, its initial value is 0, and the initial value of the communication terminal
series is set as 1. (1 for 16 bits)
2. LSB according to the frequency inverter address is MSB, and the final data MSB uses LSB to calculate CRC-16.
3. The response command of frequency inverter also has to calculate CRC-16 to be compared with CRC-16 in the
response command.
Unsigned int CRC16(unsigned char*uptr, unsigned int ulenth)
{
unsigned int crc=0xffff ;
unsigned char uindex ;
if(ulenth>=9)
{
ulenth=9;
}
while(ulenth!=0)
{
crc^=*uptr ;
for(uindex=0;uindex<8;uindex++)
{
if((crc&0x0001)==0)
{
crc=crc>>1 ;
202
Frequency Frequency
变频器 变频器
Inverter Inverter
Pb.04 Setting
Pb.04设定
Command Length
Minimum Maximum
Byte
Number Number
8
8
8
11
PLC
Response 响应
3.5char
Normal Response Length
Minimum
Byte Byte
Number
8 7
8 8
8 8
11 8
Frequency
PLC 变频器
Inverter
Command
指令
Over 5ms
5ms以上
Abnormal Response Length
Maximum Minimum
Byte Byte
Number Number
7 5
8 5
8 5
8 5
t(ms)
Maximum
Byte
Number
5
5
5
5