Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 65)

3–43 Programming and Operation
Publication 1771-UM002A–EN–P – May 2000
T = 0.1ms + (.16ms/word x number of words transferred)
The same equation is used for either read or write transfer times.
3. Calculate the worst case system time ST between transfers.
ST = PS + T(1) + T(2) + T(3) + ...
Example Problem 3
A Mini-PLC-2/15 programmable controller is controlling one 3-axis
stepper controller assembly in its I/O rack. The ladder diagram
program contains 2K words. Otherwise, this example problem is
identical to example problem 1.
Solution
1. Write down the known facts and system values.
•
Program length = 2K words
•
Processor Scan Time PS = (24ms/lK words) x (2K words) =
48ms
•
Number of words transferred W = 64 (write, 10 (read)
2. Calculate the block transfer time T for the write and read
operation.
T = 0.1ms + (.16 ms/word x 64 words) (write)
= 0.1 + 10.24
= 10.34ms (write)
T = 0.1ms + (.16ms/word X 10 words) (read)
= 0.1 + 1.6
= 1.7ms (read)
3. Calculate the worst case system time ST between two consecutive
write block transfers.
ST = PS + T (write) + PS + T (read)
= 48 + 10.34 + 48 + 1.7
= 108 ms
This is the worst case time between two consecutive write block
transfers for the Mini-PLC-2/15 controller as described in example
problem 3.