Rockwell Automation 57C570 AutoMax PC3000 User Manual - Manual (Page 58)

3Ć20
3.5 Calculating the Data Update Rate
The update rate can be calculated using the following formula:
UPDATE_TIME = (DROP_TIME X N) + NEW_DROP_TEST_TIME +
MSG_XFER_TIME
where DROP_TIME = amount of time needed for the master to
request an update and a slave to respond to the request
(2.99 ms).
N = number of slave drops (physical and virtual).
NEW_DROP_TEST_TIME = amount of time needed for the
master to poll an inactive drop and wait for its response
(2.48 ms assuming no response).
MSG_XFER_TIME = amount of time to transfer programming
terminal messages. If the master is sending a message, the
MSG_XFER_TIME is 2.09 milliseconds. If a slave is sending a
message, this time is 3.395 milliseconds.
For example, a network composed of 10 drops which is not
messaging will update each drop with a period of:
[(2.99 x 10) + 2.48] ms = 32.38 ms
The same network with slaves using messaging will update each
drop with a period of:
[(2.99 x 10) + 2.48 + 3.395] ms = 35.775 ms
The update time is not affected by how many registers are used in an
application task because all 32 input and 32 output registers are
transmitted for each active drop.
3.6 What to Do Next
Finish designing your system. For more information about the
DCSĆNET network, see chapters 7, 8, and 21, and Appendix C.