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5 Communications Timing
5-4
CJ-series User Defined CAN Unit Operation Manual for NJ-series CPU Unit (W517)
In Cyclic mode the evaluation time differs for output buffers that should be sent and for which the cyclic
time has not yet elapsed. Output buffers with elapsed cyclic time have an evaluation time of 11.6 micro-
seconds. The evaluation time will be 10 microseconds as long as the cyclic time is not reached.
The total number of output buffers is configured with message command 2902, 2903 and 2904 are
used to associate a buffer with an identifier. A buffer with an identifier associated is called a configured
buffer. The evaluation time for buffers that are not configured is 4.3 microseconds.
Example 1
•
Number of output buffers: 2
•
Number of configured output buffers: 1
Every time the configured message is sent (cyclic time elapsed), the evaluation time of all output
buffers (being 2) will be: 11.6 + 4.3 = 15.9 (microseconds)
The evaluation time is 10.0 + 4.3 = 14.3 (microseconds) in case the configured output buffer is not
sent.
Example 2
•
Number of output buffers: 640
•
Number of configured output buffers: 1
Every time the configured message is sent (cyclic time elapsed), the evaluation time of all output
buffers (being 640) will be: 11.6 + (4.3 * 639) = 2.76 (milliseconds).
Precautions for Correct Use
Precautions for Correct Use
The following guidelines apply to optimizing the evaluation time for the Cyclic Mode:
•
Set the number of output buffers with message command 2902 to the same amount as the
number of configured output buffers (that is the total number of buffers configured with mes-
sage command 2903 or 2904).
The input message process time is the time between reception of a message and the processing of that
message, i.e. data is ready to be refreshed. The process time is user dependant and can significantly
slow the process of receiving CAN messages. If processing time become excessive, messages will be
lost (and missed) due to insufficient buffer capacity.
It is strongly advised to configure the input and output buffers for CAN messages according to good
practice, as this configuration directly influences the performance of the application.
Processing Time
The process time of a received message is 65 microseconds only in the case that the message
identifier is the one corresponding with input buffer 0. The User Defined CAN Unit compares the
received identifier with the configured identifier for buffer0, next with buffer1, next with buffer 2 etc.
The comparing stops if a match between the received and configured identifier is found. Therefore
the process time will be 2.55 milliseconds if the received identifier matches with the configured iden-
tifier for buffer 639. If the received identifier is not found and a total of 640 input buffers is defined,
the process time of the message will be 2.50 microseconds.
The following guidelines apply to optimizing the process time:
SM3, Cyclic Mode
5-1-3
Input Message Processing Time
Summary of Contents for CJ1W-CORT21
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