Allen-Bradley PLC-2/30 - Page 123

Timer and Counter Instructions
Chapter 5
524
The execution time, T, in microseconds for the complete mode is:
T = 99 + 9.8 (Words operated upon per scan) + 14.4 (Number of 256
word blocks operated upon per scan)
Example: What is the execution time to perform a File-to-File AND
operation on two files 670 words long? The rate per scan is 256 and the
mode is the distributed complete mode.
T = 125 + 9.8(256) + 14.4(2) = 125 + 2509 + 28.8 = 2663
T = 2663 microseconds = 2.66 milliseconds.
The incremental mode requires approximately 100 microseconds per scan.
When the instructions are false, they require 6 microseconds.
The first scan the rung is false after the done bit is set requires 17.6
microseconds to reset flags and counters.
Table 5.G
Average
Execution Times In Microseconds For FILET OFILE AND, OR,
XOR Instructions When Instruction Is TRUE
Time (Microseconds)
Rate (Words per Scan)
Dist. Complete Mode
Complete Mode
5
10
15
25
50
100
256
512
174
223
272
370
615
1105
2648
5171
148
197
246
344
589
1079
2622
5145
Formulas for more exact approximations can be found in Section 5.6.4.
Execution time for Incremental mode is 100 microseconds per scan. When F ALSE, execution time is 6 microseconds. T ime
required to reset flags and counters is 17.6 microseconds.
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