Debugging LD programs

Debug Ladder Diagram (LD) programs to monitor the output values of elements. These values display using color, numeric, or textual values according to their data type:
  • Output values of Boolean type display using color. The output value color continues to the next input. Boolean elements remain black when the output value is unavailable. The default colors are red when True and blue when False. Customize colors for Boolean items.
  • Output values of SINT, USINT, BYTE, INT, UINT, WORD, DINT, UDINT, DWORD, LINT, ULINT, LWORD, REAL, LREAL, TIME, DATE, and STRING type display as a numeric or textual value in the element. The display value is the selected member when the output is a structure type.
ldr_db1
For structure-type variables, display one simple-type field.
The WAIT text displays in the output label when the output value for a numeric or textual value is unavailable. Transitional elements like Pulse rising edge (positive) contacts with an unstable state remain black. Values also display in the corresponding dictionary instance.
While simulating an application, debug LD programs with breakpoints, cycle-to-cycle, and step-by-step execution. Breakpoints, cycle-to-cycle, and step-by-step execution are not available while connected to controllers. Enable step-by-step execution by generating debug information for individual program organization units (POUs). The application switches to step-by-step execution upon encountering a breakpoint when debug information is generated for LD programs. Set breakpoints to rungs to instantiate step-by-step execution. The application stops upon encountering a breakpoint when debugging. At this time, the application is in the DEBUGGING state and these operations are available:
  • Step into the next rung, executes the next rung then steps into the subsequent rung. When the next rung includes a call to a function, stepping continues in the called function then returns to the next rung in the POU.
  • Step over the next rung, executes the current rung then steps to the next rung
Breakpoints appear as red circles to the left of the rung in the language editor. A yellow arrow displays on the breakpoint and the next rung highlights in yellow when the application encounters a breakpoint.
ldr_db2
The arrow points downward when stepping passes beyond the last rung of a POU.
While debugging, toggle the Boolean logical value of a selected contact, coil, or function block input.
Task
Procedure
Generate debug information for an LD POU
Only available for simulation.
  1. In the
    Application View
    , select the LD POU for which to generate debug information.
  2. In the
    Properties
    window for the POU, set
    Generate Debug Info
    to True.
Set breakpoints in an LD POU
Only available for simulation.
TIP: Setting a breakpoint in a POU during simulation checks out the POU once the simulation stops.
  1. In the
    Properties
    window for the POU, set
    Generate Debug Info
     to True.
  2. Select the rung or rungs requiring breakpoints, right-click in the rung area, and then click
    Add Breakpoint
    .
    Breakpoints appear as red circles to the left of rungs.
Remove breakpoints
Only available for simulation. Remove breakpoints in the RUNNING state or cycle-to-cycle execution while simulating.
Select the rung or rungs requiring the removal of breakpoints, right-click the rung area, and then click
Remove Breakpoint
.
Toggle the logical value of a contact coil or block input variable
Available for simulation and running online connected to controllers.
Select the required element, then right-click
Toggle Boolean Value
 (or press
Ctrl+T
).
Step into the next rung
Only available for simulation.
  • From the
    Target Execution
     toolbar, click ldr_dbsi (or press
    F11
    ).
    The program organization unit (POU) executes the current rung then steps into the next one and stepping continues in any called function before returning to the next rung of the POU.
Step over the next rung
Only available for simulation.
  • From the
    Target Execution
     toolbar, click ldr_dbso (or press F10).
    The POU executes the current rung then steps to the next one.
TIP: Set and remove breakpoints in the RUNNING state or cycle-to-cycle execution while simulating.
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