x02			c0
-----|   |---------------------(SET)------

      x02			c0
-----| / |---------------------(RST)------

      x01	c0		c1
-----|   |-----|   |-----------(SET)------

      x01			c1
-----| / |---------------------(RST)------

      c1			y0
-----|   |---------------------(OUT)------
                    _______
-------------------|  End  |--------------
                    -------
 x01 = Sensor for high water level
 x02 = Sensor for low water level
 c0  = Water level low variable
 c1  = Indicates that the we whant to fill the tank
 y0  = the actual motor that fills the tank

 Bit Sate  0    0          1    0          1    1
        --x01--x02-     --x01--x02-     --x01--x02-         
	|  |    | |     |  |    | |     |  |    | |
	|''|''''|'|     |  |    | |     |  |    | | 
	|       | |     |'''''''|'|     |       | |
	|	  |     |         |     |'''''''''|
	|_________|     |_________|     |_________|
Process State 1            2               3               
	
In process state 1 the waters sensors indicate that there are water in the tank
by being of. In process state 2 sensor x01 tells the plc that it is not touching
water we don't want to fill the tank yet. In process state 3 both x01 and
x02 tells the plc that they are not touching any water. Now we want to fill up 
the tank line 3 sees that x02 is on an that the water level low variable is on,
so it requestss for the tank to be filled by setting variable c1 to on
line 5 puts the fill motor on. As the water fills sensor x02 tells the PLC
that it sees water and turns off the water level low variable, the tank still 
fills up despite of line 3, because we set the variable c1. After 'n while
the sensor x01 sees water an turns the Fill Tank variable c1 off. And this
stops the motor in line 5.