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6.6 Precautions on RTU communications
6.6.1 Communications timing
Set a sufficient response delay to make sure that this product is switched over from transmission to
reception with regard to a high-level computer in using an RS-485.
See the figure in "6.1 Communications procedure" and "5.8 Setting a response delay."
6.6.2 Interval between requests
In transmitting a series of "request messages" from a high-level computer, allow for an interval of
2msec or more from the reception of a "response message" from this product to a next
transmission.
6.6.3 Response conditions
If there is a time interval of 3.5 characters or more between data items constituting a "request
message," this product cannot recognize it as a "request message." It will therefore not return a
"response message." If, therefore, the "request message" contains an error, this product will not
return a "response message" (error reply) containing an ERR unless the above conditions are met.
Therefore, the high-level computer transmits the necessary "request message" again if a "request
message" is sent to this product but the latter does not return a "response message" at the end of an
appropriate period.
The moment a period of 3.5 characters or more has elapsed, it clears all codes received before that.
6.6.4 Errors in address specification
This product will not respond to any "request message" that specifies an address other than that
specified for itself. If, therefore, the address portion of a "request message" is error-ridden, none of
the mobile units will return a "response message."
Therefore, the high-level computer transmits the necessary "request message" again if a "request
message" is sent to this product but the latter does not return a "response message" at the end of an
appropriate period.
6.6.5 Number of digits in data and the decimal position
See "6.5 Description of RTU codes, g) Data portion."
6.6.6 Operation after receiving a store request message
This product starts to store data after correctly receiving a store request message from a high-level
computer.
This product only stores data different from the contents of the EEPROM (data that is changed).
The time (TW) required for storing data is within 6 seconds.
This product transmits a storage-complete reply after the data is stored.
This product will not guarantee that the data is stored if this product is turned off during a storage
operation. Do not turn off this product for 6 seconds after transmitting a store request message.
6.6.7 Operation after turning on the power
This product will not perform communications (no response) for about 4 seconds after it is turned
on. Allow for a delay until communications is started after this product is turned on.
6.6.8 Storing data other than a store request message
In the two cases described below, the unit stores the parameter to EEPROM even if no store
request message is received.
1) If a parameter is changed by key operation, writing will be done only for the changed
parameter and the related parameter.
2) If auto-tuning is started and ends normally, writing will be done only for the PID constant.
6.6.9 Changing the setting (SV) by communications during auto-tuning
Even if the setting (SV) used in control for auto-tuning are changed by communications, the setting
(SV) will not be changed until the auto-tuning ends.