There are several types of ports in eXpress. Each port type signifies a particular direction or type of information / signal flow. Most commonly, objects have both input and output ports, although it is possible to have objects with only one or the other. Each port type is listed in the following table, along with an icon showing how it appears on a design:
Input
A standard input port (where signals enter the object).
Output
An output port (where signals emerge from the object).
Bidirectional
A port that is both an input and output.
Control
An alternative type of input port that is used to represent inputs that do not contribute to the creation of an active function. Usage of this type has diminished in the life of eXpress due to other features added which make the use of the control port less important.
Unused
A completely non-functional port (equivalent to an unused "pin").
