Scan Time Worksheet - Allen-Bradley MicroLogix 1100 Instruction Set Reference Manual

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462 MicroLogix 1100 Memory Usage and Instruction Execution Time
MicroLogix 1100

Scan Time Worksheet

Input Scan (sum of below)
Overhead (if expansion I/O is used)
Expansion Input Words X 3 µs (or X 7.5 µs if Forcing is used)
Number of modules with Input words X 10 µs
Program Scan
Add execution times of all instructions in your program when executed true
Output Scan (sum of below)
Overhead (if expansion I/O used)
Expansion Output Words X 2 µs (or X 6.5 µs if Forcing is used)
(1)
Communications Overhead
Worst Case
Typical Case
Use this number if the communications port is configured, but not communicating to
any other device
Use this number if the communications port is in Shutdown mode
System Overhead
Add this number if your system includes a 1764-RTC, 1764-MM1RTC, or MM2RTC. = 80 µs
Add this number if your system includes a 1764-DAT
Housekeeping Overhead
Totals
(1) Communications Overhead is a function of the device connected to the controller. This will not occur every scan.
Publication 1763-RM001C-EN-P - October 2009
Calculate the scan time for your control program using the worksheet
below.
Pick one of the four numbers for Channel 0
Pick one of the four numbers for Channel 1
Multiply by Communications Multiplier from Table X
= 53 µs
=
=
Input Scan Sub-Total =
=
Program Scan Sub-Total =
= 29 µs
=
Output Scan Sub-Total =
= 1100 µs
= 400 µs
= 150 µs
= 0 µs
Communications Overhead Sub-Total =
= 530 µs
= 240 µs
System Overhead Sub-Total =
Sum of all
Time Tick Multiplier (X1.02)
Total Estimated Scan Time =
240