': trans atob (1) : decision_lose_the_frame('No' instead of: trans atob (1) : decision_lose_the_frame('No') trans atob (1) : decision_lose_the_frame( ('yes') You can add several filter conditions and manage them with Edit > Filter Conditions. To enter a filter condition with this command, do not type the keyword filter in front of the condition. Filter conditions are also active during random and exhaustive simulation, where they are very handy to guide the simulation automatically. In such modes, the transitions fired are selected by the Simulator, not by you; thus, you must filter a certain transition if you do not want the Simulator to fire it. 104 Validation of Communications Systems with SDL We have seen how to filter a certain transition (filter trans...), but the argument of the filter command can also be an expression or an event. Here are some examples. To prevent from firing any transition leading to variable n320cnt > 2 (simulation will only be possible for values 0, 1 and 2): filter n320cnt > 2 To prevent any output of signal L_EstabInd: filter output L_EstabInd To limit to 2 signals the content of the input queue of instance 1 of process DLC in block DLCa (the part is_active is not necessary for a process instance that always exists, such as dispatch(1)) filter is_active (DLCa!DLC(1) ) and \ length (DLCa!DLC (1) queue) > 2 To prevent instance 1 of process DLC in block DLCa from reaching the state connected: filter DLCa!DLC(1) !state = connected To block all the transitions contained in the block DLCa: filter trans DLCa 4.3.7.10 Undo and redo Simulator commands Undo enables you to go back to any previous simulation step; then you can use redo to replay the previously undone steps. Redo is also used to replay a loaded scenario. Two buttons in the Simulator perform undo and redo of one step at a time: K and To undo or redo a larger number of steps, you can use the textual commands undo and redo. For example, if you are at Step 27, you can type: undo 16 returns to step 27 - 16 = 11 redo 8 - - returns to 