Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 298)

Publication 1785-UM012D-EN-P - July 2005
C-12 Maximizing System Performance
The worst-case controller time is:
For a 3-rack system with a 20 ms program scan, the worst-case controller time
is: 10 + 20 + 20 + (0.18
∗ 3) = 50.54 ms.
Example Calculation Based on the results of each throughput component calculation presented
within the chapter, an example of a worst-case update time calculation is:
Performance Effects of
Online Operations The performance of the PLC-5 controller is affected when you perform online
operations via a DH+ link to your program files while in Run mode. Affected
activities are:
• DH+ messages
• serial port messages
• channel 3A messages
• remote block-transfers
Variable Value
periodic input buffer update from remote I/O
buffer 10 ms
one program scan to guarantee inputs received xx ms
one program scan to guarantee outputs received xx ms
0.18 ms times number of racks xx ms
total
Variable Value
input card delay 10 ms typical
I/O backplane 1 ms
worst-case remote I/O scan time 30 ms
worst-case controller time 50.54 ms
worst-case remote I/O scan time 30 ms
I/O backplane 1 ms
output card delay 1 ms typical
total 123.54 ms