Rockwell Automation 1771-DA,D17716.5.13 U MNL 1771-DA ASCII I/O MODULE - Manual (Page 182)

ASCII Module
PLC-2 Family Processors
Appendix A
AĆ14
1. Calculate the block transfer time T for the read and write operation.
T = 0.1ms + (6.16ms/word x number of words transferred)
The same equation is used for either read or write transfer times.
2. Calculate the worst case system time ST between two read block
transfers.
ST = PS + T(read) + PS + T(write)
Example Problem 3
A Mini-PLC-2/15 programmable controller is communicating with one
ASCII module in its I/O chassis. The ladder diagram program contains
2K words. Otherwise, this example problem is identical to example
problem 1.
Solution
The facts of the problem are:
Program length = 2K words
Processor Scan Time PS = (24ms/1K words) x (2K words) = 48ms
Number of words transferred W = 64(read), 2(write)
1. Calculate the block transfer time T for the read and write operation.
T = 0.1ms + (0.16ms/word x 64 words)(read)
= 0.1 + 10.24
= 10.34ms (read)
T = 0.1ms + (0.16ms/word x 2 words)(write)
= 0.1 + .32
= 0.42ms (write)
2. Calculate the worst case system time ST between two consecutive
read block transfers.