Mitsubishi Electric FR-A800, Instruction Manual

Page: 812 / 1042

(N) Operation via communication and its settings Parameters
5 - 632
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Data check time
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Query
A message is sent to the slave (for instance, the inverter) having the address specified by the
master.
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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.
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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.
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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.
Message frame (protocol)
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Communication method
Basically, the master sends a Query message (question), and slaves return the 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), bit7 (= 80 h) of the
Function Code is turned ON, and the error code is set at Data Bytes.
Item Check time
Various monitors, operation command, Frequency setting (RAM) < 12 ms
Parameter read/write, Frequency setting (EEPROM) < 30 ms
Parameter clear / all clear < 5 s
Reset command No answer
Tab. 5-280: Data check time
NOTE During broadcast communication, functions are executed regarded of the set inverter station
number (Pr. 331).
I001228E
Fig. 5-317: Data transmission
Query message from Master
Device Address Device Address
Function Code Function Code
Eight-Bit
Data Bytes
Eight-Bit
Data Bytes
Error Check Error Check
Response message from slave