EM11 User’s Manual
Appendix I
135
response to the data.
Here, master is personnel computer (PC), industrial machine or programmable logical controller (PLC),
and the slave is inverter. Master not only visits some slave, but also sends the broadcast information to all
the slaves. For the single master “Inquiry/Command”, all of slaves will return a signal that is a response;
for the broadcast information provided by master, slave needs not feedback a response to master machine.
Communication data structure
Modbus protocol communication data format of EM11 series inverter is shown as following. The inverter
only support the reading and writing of Word type parameters, the corresponding reading operation
command is “0x03”, the writing operation command is “0x06”. The writing and reading operation of byte
or bit is not supported.
In theory, the host computer can continuously read several function codes once (that is, the maximum value
of “n” is 12), but note that not to jump across the last function code in this function group to avoid the
wrong reply.
Appendix I
EM11 User’s Manual
136
If the wrong communication frame was detected by the salve or other reasons caused the failure of reading
and writing, the wrong frame will be replied.
RTU frame format
Frame start (START)
More than the 3.5- character time
Slave address(ADR)
Communication address:1 to 247(0: broadcast address)
Command code(CMD)
03: Read slave parameters
06: Write slave parameters
Function code address(H)
It indicates the external parameter address of frequency inverter in
hexadecimal format;
There are functional code or non-functional code (such as running state
parameter/ running command parameters) type parameters, for details
see the address definition.
During the transmission, high bit is put in the front, and low bit is at the
back.
Function code address(L)
Number of function code(H)
It indicates the number of function code ready by the frame. If it is “1”,
then it indicates that it reads one function code. During the transmission,
high bit is put in the front, and low bit is at the back.
Only one function code can be modified at one time without the field.
Number of function code(L)
