The GPIO connection allows up to 4 inputs, 4 outputs and supplies +24 VDC for external sensors and signaling devices. The GPIO interface is electrically isolated from the reader's chassis ground, but its ground is common to the power return of the 24 VDC external supply when this is present.
GPIO signals allow some flexibility. Inputs are pulled up within the reader to +5 VDC and can be shorted to ground to pull them low. They are broadly compatible with industrial sensors with NPN outputs and may be connected directly to relays or switch contacts. Alternatively, they can be driven by 5V logic. In the low-state logic, the current source from the reader is approximately 3 mA, so standard gates in most logic families can drive them directly. Current flow in the logic high state is close to zero. The general-purpose outputs are open-drain (NPN type) drivers, pulled up to 5V. Each output can withstand voltages up to +30 VDC but should not be driven negatively. Drive 24V relays, indicator lamps, etc., by wiring them between the +24 VDC supply pin and the general-purpose output pins. Although each output can sink up to 1A, the maximum current drawn from the internal 24V supply is 1A, so use an external power supply if the current requirements exceed this. Note that the state of the general-purpose outputs is inverted; for example, driving a control pin high at the processor pulls the corresponding output low.
