Omron CJ1W-PRT21 Operation Manual page 32

Performance
PROFIBUS-DP cycle time
PLC cycle time
I/O Refresh Time
The overall PROFIBUS-DP communication cycle time will depend on the
number and types of PROFIBUS-DP master(s) and other slaves connected to
the network, and the overall bus parameters defined in the configuration of
the master unit(s).
The time required to exchange I/O data between the CJ1W-PRT21 and its
master will depend on the number of input and output words defined in the
master's configuration, the selected baud rate, and on the performance of the
master unit itself.
The minimum time interval between subsequent I/O data exchanges with the
CJ1W-PRT21 (minimum slave interval) is 0.5 ms as defined in the Unit's GSD
file.
The host PLC's cycle time mainly depends on the size of the PLC program
and the I/O refresh times of all I/O Units on its backplanes. The size of the
PLC program is application specific. Besides optimising the PLC program, the
program execution time can only be decreased by using a faster CPU Unit.
The total I/O refresh time depends on the types of Units that are mounted. Not
all Units refresh the same amount of data. The I/O refresh time of the CJ1W-
PRT21 depends on the number of I/O data words that have been mapped.
For the CJ1G CPU45:
I/O Refresh Time = n x 1 µs.
n = number of I/O data words
Maximum words = 184, so maximum I/O refresh time becomes 184 x 1 µs =
0.184 ms
Section 2-3
13