The main source of signals and data for the controller are ports. There are different types of ports: binary (eg, relay control or "dry contacts"), measuring ports (e.g. for measuring voltage, current, frequency, etc.), specialized ports (e.g., proximity-card reader access control system or data ports human-machine interface (HMI)) and virtual (which provide results of formulae calculation conducted by the mathematical module).
Binary ports are the ports that capture one of two states (on / off, open / closed). Such ports are managed relay contacts, "dry contacts" or various signaling for logic states of peripheral devices. Binary ports with an additional subtype "dry contact" can be separately classified by their normal status: "normally closed" or "normally open". This status informs the controller regarding the main port state. A "normally closed" port in its normal state has electric current with the voltage equating or higher than the "logical one" flowing through it.
A measuring port signals about changing of conditions and provides the measurement data given by the connected to it device, sensor or mechanism. The data coming from the port may be in the same units as it was measured or can be recalculated by the functionality in the microcontroller in this device.
Ports can be built-in in the controller (internal) or external. External ports "are rendered" by digital devices: immediate regional devices, peripheral sensors, or actuators. Number of external ports that are "announced" to logic controllers shouldn't necessarily be the same as the number of physical terminals. Part of peripheral ports can be logical that do not involve actual physical connections.
The frequency of data acquisitions from ports is configured via the controller's settings for each port, except for binary. Data for binary ports is acquired many times per second (at least several times per second - each), so there is no time interval option available for this type of ports.