Parking Barrier

If anyone help me, I have to do a Ladder Program of a Parking Lot with a capacity of 20 cars. When a car drive in to the parking Lot a sensor (input1) lift a barrier and keep it up for 20 seconds and then takes its original position, when a car want to exit the parking, another sensor (input2) lift anopther barrier and keep it up too for 20 seconds. The important thing is when the capacity comes to 20 cars, the system must disabled.
Ok Thanx

Your homework will require you to learn how to use timers and counters. Post your efforts here for specific questions. In general, we don't give students outright code for their homework.

Step one is creat a point list - a list of all the inputs and outputs for the PLC, including location, voltage, type and description.

Step two is creat a text version of the program operation, similar to your question but in greater detail and tied to specific events.

Step three is create a list of all alarms and messages you need the PLC to trigger.

Step four is identify all operator interface requirements.

Step five is to start writing code, one function at a time. Don't try to figure it al out at once - start writing and the additional functions will come as they are needed. Comment thouroughly, and use clear and concise nicknames for your I/O and internal bits and registers.

Step six through whatever is to test and revise.

Way to go Tom!