Omron CJ1W-CORT21 Operation Manual page 113

Maximum I/O Response Time
CPU
CORT21
Bus
Input node
Output node
t
IN
t : Input Node ON (OFF)
IN
t : Output Node ON (OFF) delay
OUT
t : Message Delay time
MD
The unit processing time of messages to be transmitted depends on the number of send triggers
and the (send) mode of each output buffer. If many send triggers change at (or near) the same time,
or if many output buffers are changed at the same time, or have the same time triggering, the trans-
mission of output buffers will queue causing a delay in transmission. If the rate at which the output
buffers change state requires a higher transmission rate than the unit is capable of (see 5-1-4 CAN
Interface), a transmit queue overflow occurs.
Transmit queue overflow errors can be solved by reducing the rate at which the output buffers
change state and therefore requests for transmission are generated.
Receive queue overflow errors can be solved by decreasing the CPU cycle time or by reducing the
rate at which the other units transmit messages.
In case of high bus loads (over 50%), additional delays can be caused by high-priority (low identifier)
messages which delay the transmission of lower priority messages.
Additional Information
The CPU Unit's task period is the sum of the User Program execution time plus the User Defined
CAN Unit's refresh time on the CPU Unit.
CJ-series User Defined CAN Unit Operation Manual for NJ-series CPU Unit (W517)
t t t
MD UPR PE
maximum I/O response time
delay t
UPR
t
UPT
t
PE
t
RF
5 Communications Timing
t t t
RF PE RF
: Unit Processing time for Received messages
: Unit Processing time for Transmitted messages
: Program Execution time
: I/O Refresh time
t t t
UPT MD OUT
5
5-7