Emheater EM12 Series, User Manual

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Appendix I EM12 User’s Manual
122
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 EM12 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.
Target
station
address
Read the
command
(0x03)
Function code
address
(H
……
L)
Number
of
function
code(n)
CRC
correction and
L
……
H
Free
>3.5Byte 1Byte
1Byte
2Byte 2Byte 2Byte
Calculate CRC
correction
Master reads
command frame
Free
(Start frame)
Target
station
address
Read the
command
(0x03)
Function code
address
(H
……
L)
Number
of Data
type(2n)
CRC
correction and
L
……
H
Free
>3.5Byte 1Byte
1Byte
(2n)Byte 1Byte 2Byte
Calculate CRC
correction
Free
(Start frame)
Slave reads
response frame
Target
station
address
Write the
command
(0x06)
Function code
address
(H
……
L)
CRC
correction and
L
……
H
Free
>3.5Byte 1Byte
1Byte
2Byte 2Byte
Calculate CRC
correction
Master writes
command frame
Free
(Start frame)
Function code
parameter
(H
……
L)
2Byte
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.