A simple common anode 7 segment display could be interfaced to a micro- pin or peripheral interface adaptor (PIA), if for example each segment of the display requires 10-15mA to run it, an I/O pin may not be able to source enough current on it’s own, so a buffer or current amplifier must be used like the one shown below. One configuration is using logic gates as current amplifiers, the ones used here are quad 2 input nand gates the 7401, which provide 4 gates in one chip. So if a logic high is provided on the PIA , I/O or micro pin the nands output will be logic low. Because the 7 segment is common anode, this allows current to flow from the power supply and through the leds and series resistors and the 7401 sinks the current of 15mA if the resistors are 200R. The 7401 can not source 15mA on each pin but can sink this amount, so this configuration would work.