Mitsubishi Electric FR-A820-00046 (0.4K) Instruction Manual page 655

• Query
A message is sent to the slave (the inverter) having the address specified by the master.
• Normal response
After the query from the master is received, the slave executes the request function, and returns the corresponding normal
response to the master.
• Error Response
When an invalid function code, address or data is received by the slave, the error response is returned to the master.
This response is appended with an error code that indicates the reason why the request from the master could not be
executed.
This response cannot be returned for errors, detected by the hardware, frame error and CRC check error.
• Broadcast
The master can broadcast messages to all slaves by specifying address 0. All slaves that receive a message from the
master execute the requested function. With this type of communication, slaves do not return a response to the master.
NOTE
• During broadcast communication, functions are executed regarded of the set inverter station number (Pr.331).
 Message frame (protocol)
• Communication method
Basically, the master sends a query message (inquiry), and slaves return a response message (response). At normal
communication, the device address and function code are copied as they are, and at erroneous communication (illegal
function code or data code), bit 7 (= H80) of the function code is turned ON, and the error code is set at data bytes.
Query message from Master
Device Address
Function Code
Eight-Bit
Data Bytes
Error Check
Message frames comprise the four message fields shown in the figures above.
A slave recognizes message data as one message when a 3.5 character long no-data time (T1: start/end) is added before
and after the data.
• Details of protocol
The following table explains the four message fields.
Start
Start
T1
654
5. PARAMETERS
5.15 (N) Communication operation parameters
Device Address
Function Code
Error Check
Response message from slave
Address Function
ADDRESS FUNCTION
8 bits 8 bits
Eight-Bit
Data Bytes
Data
DATA
n × 8 bits
CRC check
CRC CHECK
L H
T1
8 bits 8 bits
End
End