Performance; I/O Refresh Time; Output Message Evaluation Time - Omron CJ1W-CORT21 Operation Manual

5 Communications Timing
5-1

Performance

The overall performance of the User Defined CAN Unit depends on the performance of the host CPU
interface and the performance of the CAN interface. In the next two sub-sections, these factors will be
described.
5-1-1

I/O Refresh Time

The I/O refresh time of the User Defined CAN Unit depends on the size of the receive flags area, the
size of the send trigger area, on the number of input buffers and on the number of output buffers that
have been defined. Refer to Section 3, Data Exchange with the CPU Unit and Section 4, Message
Communications for more information.
5-1-2

Output Message Evaluation Time

The output message evaluation time is the time between completion if the I/O refresh of the unit and the
moment an output message is set ready for sending. The duration of this period is user-dependent and
can introduce a significant delay before the message is actually sent. The message evaluation time
depends on the length and structure of the user program and the send mode used for the User Defined
CAN Unit. It is advised to review the timing, as the performance of the complete system (or application)
is directly related to this timing. The evaluation time depends on the send mode used, and as different
send modes can be combined, the total evaluation time is the sum of the individual send mode evalua-
tion times.
Precautions for Correct Use Precautions for Correct Use
• Sending messages in the Triggered mode is the fastest way to send messages. It is faster
than evaluation in the On Change mode and Cyclic mode.
• Sending messages in Cyclic mode is more than 4 times faster than when in On Change mode.
.
SM1, Triggered Mode
The evaluation time in Trigger mode differs with the state of the trigger (the trigger can be OFF or ON).
When the rising edge of the trigger is detected, the message in the output buffer is sent.
Every time the trigger is detected and the message is sent, the evaluation time is 10 microseconds. The
evaluation time is 9 microseconds every time the trigger is OFF.
The total number of output buffers is configured with the message command 2902. Message command
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.
The following examples are provided for calculation of the evaluation time.
Example 1
• Number of output buffers: 2
• Number of configured output buffers: 1
Every time the trigger of the configured message is ON, the evaluation time of all output buffers
(being 2) will be: 10.0 + 4.3 = 14.3 (microseconds).
The evaluation time is 9.0 + 4.3 = 13.3 (microseconds) for the configured output buffer, in case the
trigger is OFF.
5-2
CJ-series User Defined CAN Unit Operation Manual for NJ-series CPU Unit (W517)