Rockwell Automation 1771-DE Absolute Encoder Module User Manual - Manual (Page 46)

Appendix A
AĆ5
1. Calculate the system values that are determined by the system
configuration.
Program Scan (PS) = (5 ms/1K words) x (number of program
words)
Processor I/O Scan (PIO) = (1 ms/rack number) x (number of
declared rack numbers)
Number of words transferred (W) = 2 (read) or 20 (write)
2. Calculate the block-transfer time (T) for the read or write operation.
T = 0.08 ms/word x number of words transferred
3. Calculate the worst case system time (ST) between transfers.
ST =PS + PIO + T(1)(read) + T(2)(read) +T(3)(read) +...
PS + PIO + T(1)(write) + T(2)(write) + T(3)(write) +...
=2(PS + PIO) + T(1)(read) + T(2)(read) + T(3)(read) + ...
T(1)(write) + T(2)(write) + T(3)(write) + ...
Example 2
A PLC-2/30 programmable controller is controlling four I/O racks
in a local configuration. Assume one block-transfer module per
chassis and one assigned rack number per chassis (Figure A.2).