Table of Contents
Advertisement
Appendix A
Block transfer Timing for PLC 3
Family Processors
A 8
The same equation is used for read and write transfer times.
2.
Calculate the worst case system time (ST) between two
block-transfer-read operations.
ST
=PS + PIO + T(read) + PS + PIO = T(write)
Example 3
A Mini-PLC-2/15 programmable controller is communicating with
one encoder module in its I/O chassis. The ladder diagram
program contains 2K words.
Solution:
The facts are:
Program length = 2K words
Processor scan time (PS) = (15 ms/1K words) x (2K words) = 30
ms
Processor I/O scan time (PIO) = 5 ms
Number of words transferred (W) = 2 (read), 20 (write)
3.
Calculate the block-transfer time (T) for the read and write operation.
T
=0.08 ms/word x 2 words (read)
=0.16 ms (read)
T
=0.08 ms/word x 20 words (write)
= 1.6 ms/(write)
4.
Calculate the worst case system item (ST) between two consecutive
block-transfer-read operations.
ST
=PS + PIO + T(read) + PS + PIO + T(write)
=30 + 5 + .16 + 30 + 5 + 1.6
=71.76 ms
This is the worst case time between two consecutive block-transfer-read
operations for the Mini-PLC-2/15 controller.
The execution time required to complete a block-transfer-read or -write
operation with a PLC-3 family processor depends on the number of:
words of user program
active I/O channels on the scanner
Advertisement
Table of Contents
