bmw?
Here's a solution in Logix5000 using just two instructions...
Prize for the first person to correctly work out how it can be done....
Periodic Tasks?
The 2000mS task must have the higher priority. It will alternate between executing alone and executing along with the 4000mS. When they execute together, the 4000mS must go second and "overwrite" the action of the 2000mS.