Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 63)

3–41 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
3. Calculate the block transfer time T for the read and write
operation.
T = 0.1ms + (.075ms/word x number of words transferred)
The same equation is used for either read or write transfer times.
4. Calculate the worst case system time ST between transfers.
ST = PS + PIO + T(1) + T(2) + T(3) +...
Example Problem 2
A PLC-2/30 programmable controller is controlling four I/O racks in
a local configuration (Figure 3.19). Otherwise this example problem
is identical to example problem 1.
Figure 3.19
Local System Example
1771–AL
1771–QA
Rack No. 1
1771–AL
1771–QA
Rack No. 2
1771–AL
1771–QA
Rack No. 3
1771–AL
1771–QA
Rack No. 4 10536
PLC–2/30
Solution
1. Write down the known facts.
Program length = 4K words
Number of chassis = 4 rack numbers
Number of default block transfer words = 64 words (write),
10 words (read)
2. Calculate the system values.