Emerson DSM314 - Appendix E: Local Logic Execution Time; E-1 Local Logic Execution Timing Data

User Manual Appendix E
GFK-1742F Jan 2020
Local Logic Execution Time 450
Appendix E: Local Logic Execution Time
This appendix contains information necessary to determine a local logic program’s
execution time.
E-1 Local Logic Execution Timing Data
Local Logic program in the DSM is constrained to complete execution within 300
Microseconds. Exceeding the execution time limit will result in a watchdog timeout and an
error being reported. The watchdog timeout error will stop axes motion and Local Logic
execution. The timing data supplied in the tables below allows the programmer to compute
the worst-case execution time for a program. Note that the data below represents
execution times, not response times. For example, the execution time required to write a
value to the follower ratio variables is 0.30 microseconds, however the time required to
observe the resulting change in the axes motion would be in the order of
2 to 5 milliseconds. Similarly, for the digital inputs the hardware filter delays must be taken
into account when computing the response time.
Note: If the program execution time is between 300 and 350 microseconds a watchdog timeout may
not occur, depending on the task loading in the module. The user should keep his program
execution time within 300 microseconds to ensure that it runs without any timeouts.
The tables below can be used to compute the worst case execution times and therefore
predetermine that a program will not cause a watchdog timeout. The examples below
illustrate the computation of execution times for a program.
E-2 Example 1
Execution Time for Instruction Line 1=>
(Time to Load P002) + (Time to load Constant) + (Time to perform Addition) + (Time to write
P001)
=> 0.60 (from Table 97) + 0.50 (from Table 97) + 0.90 (from Table 91) + 0.60 (from
Table 97)
=> 2.60 microseconds
Execution Time for Instruction Line 2 =>
(Time to Load P001) + (Time to load Constant) + (Time to perform > Conditional)
=> 0.60 (from Table 97) + 0.50 (from Table - 97) + 2.50 (from Table 92)
=> 3.60 microseconds