Turning Output on/off every duty cycle

I am programming a Unitronics vision 570 PLC using Visilogic. I have a heater physically hooked up to an output. What must I do in the ladder diagram to ensure the heater is on/off every duty cycle?
Or
What functional block logic do I need to use so heater turns on when I press a button.Any help will be appreciated.

How are you going to determine when the heater will be on or off depending on your duty cycle?

Do you want times to be added on to the screen for on/off?

A little more detail would help a lot.

Mark

every scan cycle is done with
out:= NOT out;