1766-RM001A-EN-P MicroLogix 1400 Programmable Controllers ...

550 MicroLogix 1400 Memory Usage and Instruction Execution TimeMicroLogix 1400Scan Time CalculationThe following is an example of how to calculate a typical scan time for aladder program. In this example, a program scan time of 15.0 ms isassumed. The program scan time includes the system overhead time.Communication Channels InactiveProgram scan time: 15 msSystem overhead: 3.35 ms (typically 20% of program scan time)Ladder logic execution time:program scan time - system overhead = 15 - 3.35 = 11.65 msOne Or More Communication Channels ActiveWhen any of the channels are active, the following typical overheadsshould be taken into account:• Channel 0 overhead: 0.8 ms• Channel 1 overhead: 0.4 ms• Channel 2 overhead: 0.7 msIf Channel 1 is active and the other two channels are inactive, totalprogram scan time is:Program scan time (when no communication channels active) +Channel 1 overhead = 15 ms + 0.4 ms = 15.4 msIf all Channels are active, total program scan time is:Program scan time (when no communication channels active) +Channel 0 overhead + Channel 1 overhead + Channel 2 overhead =15 ms + 0.8 ms + 0.4 ms + 0.7 ms= 16.9 msPublication 1766-RM001A-EN-P - October 2008