Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 416)

Appendix B
Programming Reference
B–21
Estimating Memory Usage for Your Control System
Use the following to calculate memory usage for your control system.
1. Determine the total instruction words used by the instructions in
your program and enter the result. Refer to the table on page B–16.
2. Multiply the total number of rungs by 0.75 and enter the result.
Do not count the Start of File or End of File screens in each file.
3. To account for controller overhead, use 177.
4. To account for application data, use 110.
5. Total steps 1 through 4. This is the estimated total memory usage of
your application system. Remember, this is an estimate, actual
compiled programs may differ by
±
12%.
Subtract the total memory usage from 1024.
The result of this calculation is the estimated total memory
remaining in your selected controller.
Important: The calculated memory usage may vary from the actual
compiled program by
±
12%.
Total Memory Usage:
6. To determine the estimated amount of memory remaining in the
controller you have selected, do the following:
177
110
1024
-
Total Memory
Remaining:
Total Memory Usage
(from above):
Execution Time Worksheet
Use this worksheet to calculate your execution time for logic program.
Procedure Maximum Scan Time
1. Input scan time, output scan time, housekeeping time, and forcing.
2. Estimate your program scan time:
A. Count the number of program rungs in your logic program and multiply by 6.
B. Add up your program execution times when all instructions are true. Include interrupt routines in
this calculation.
➀
3. Estimate your controller scan time:
A. Without communications, add sections 1 and 2
B. With communications, add sections 1 and 2 and multiply by 1.05
4. To determine your maximum scan time in ms, divide your controller scan time by 1000.
210
µ
s (discrete)
330
µ
s with forcing (analog)
250
µ
s without forcing (analog)
________
_________ ms
_________
µ
s
_________
µ
s
_________
_________
µ
s
➀ If a subroutine executes more than once per scan, include each subroutine execution scan time.