With multi-segment displays, what you see ... at least in the Arduino world; the segments need +1.5 volts with reference to the common connection to turn on, and -1.5 volts to turn off.

What do you do with 144 7-segment displays? If you’re [Frugha] you ... as [Frugha] wanted to control the clock with a single Arduino Nano. Even charlieplexing won’t get you that many I/O ...