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3.3.4
Things to Be Noted During MODBUS RTU Communication
3.3.4.1
Timing of Transmission
Upon using RS-485, set enough response delay time to ensure communication (sending/receiving) with the upper
computer.
See the figure
3.3.4.2
Request Interval
If
“
request message
”
is to be sent continuously by the upper computer, wait for at least 2 msecs. from the arrival of the
“
response message
”
from this product before sending the next request message.
3.3.4.3
Conditions for Response
This product will not return the
“
response message
”
if there is a time interval of more than 3.5 characters between data
that comprise the
“
request message
”
since it cannot identify these data as one whole
“
request message
.”
Therefore, although there is an error in the
“
request message
,”
a
“
response message
”
with the error number (response
for the error) will not be returned unless the above condition is met.
Therefore, the upper computer should resend the necessary
“
request message
”
if the
“
response message
”
is not returned
within the reasonable time.
At a time interval of more than 3.5 characters, this product clears all characters that were received prior to the said
interval.
3.3.4.4
Address Specification Error
This product will not respond to any
“
request message
”
that specifies an address other than the one that has been set to
itself.
Therefore, if there is an error in the address section of the
“
request message
,”
none of the slave stations will return the
“
response message
.”
Therefore, the upper computer should resend the necessary
“
request message
”
if the
“
response message
”
is not returned
within the reasonable time.
At a time interval of more than 3.5 characters, this product clears all characters that were received prior to the said
interval.
3.3.4.5
Number of Digits of Data and Position of Decimal Point
See
Explanation of MODBUS RTU Codes g) Data Section
.”
3.3.4.6
Operation After Receiving the Save Request Message
This product starts saving data once it receives the save request message correctly from the upper computer.
Data will be saved within six seconds.
The product sends a response when the saving of data is completed.
Some data may be lost if the product is turned OFF while the saving process is in progress.
Do not turn the power of this product OFF for at least six seconds after the sending of the save request message.
3.3.4.7
Upon Turning the Power ON
This product will not perform any communication while performing an initial process after turning its power ON (no
response).
Set the adequate time of delay from power ON to the start of communication.
3.3.4.8
Saving the Data Other Than Save Request Message
This product saves the parameter into the memory element even without receiving the save request message in case of
the following:
① When the parameter has changed by the key operation and when the limiter of other param
eters has become
active because of the changed parameter
② When auto tuning/self
-tuning has ended successfully
