Safety Considerations Guide for Trident v2 Systems - TUV ...

Array Index Errors
Infinite Loops
Development Guidelines 47
If an array index error is detected during runtime, the default behavior is to trap. This results in
the Trident controller going to the safe state, with all outputs de-energized.
If your application requires some other behavior, you can use a CHK_ERR function block to
detect the error, and a CLR_ERR function block to clear the error and prevent a trap.
Note If an array index is too small or too large, the array operation is performed on the last
element of the array. Array bounds checking is always turned on—there is no means to
disable the array index checking.
See the TriStation 1131 Libraries Reference for more information about the CHK_ERR and
CLR_ERR function blocks.
If the actual scan time exceeds the maximum allowable scan time for the Trident controller, the
main processors will reset, causing the Trident controller to go to the safe state, with all outputs
de-energized. The maximum allowable scan time for the Trident is 450 milliseconds.
Although it is not possible to program an endless loop with TriStation 1131 software, it is
possible to create a loop with a very long time, enough to increase the actual scan time beyond
the controller’s maximum allowable scan time.
See Setting Scan Time on page 49 for more information about actual and maximum scan times.
Safety Considerations Guide for Trident v2 Systems