The NL501 Logic Gate module contains two logic gates each with two inputs and complementary outputs. Both of these gates can be independently configured by PCB mounted switches as either 2-input AND gates or 2-input OR gates. The open circuited inputs are automatically held low for the OR function or high for the AND function and a further switch allows expansion of the second gate to take the output of the first as a third input. This enables a 4-input AND gate or a 4-input OR gate to be realised. A further possibility is a 3-input AND or OR gate where one of those inputs is a 2-input OR or AND function from the other gate. Provision is made for input 1 of gate 1 to be connected to the output of the NL501 Logic Gate module to the left and all 4 outputs are available for selection as the output to the module to the right. This is done by jumper plugs at the rear of the PCB.