So I know to drive a 7-segment display you need a TON of pins. However there are 7-segment display drivers (such as the MAX7219) that seem pretty popular.
However I'm looking at the datasheet, and am a bit confused. (https://datasheets.maximintegrated.com/en/ds/MAX7219-MAX7221.pdf). It mentions the SEG A-G connecting to the obvious segments of the 7-segment display (AND2307SLC mentioned in the datasheet)...but what exactly are the DIGI 0-7 for then? (But then on page 13 it shows them actually connected.)
Maybe I'm a bit confused how it works exactly. From my vague understanding we send it serial data to the DIN pin of what segment we want to display, and it outputs that to SEG A-G. (We send 16 bits, and it only looks at the last 4 correct?) (BTW this makes me not understand what LOAD is for exactly.)
And then there is decode mode, which I guess is the main way to turn on digits via serial as opposed to just turning them on via DIG7-DIG0.
Am I even on the right track on this? I'm just a bit confused how it all works together. Also I'm curious how it handles turning on multiple segments when doing it via serial. Is it storing something in SRAM and then uses some sort of timer/refresh to keep the digits on?
Thanks, it's just sort of an interesting chip that I'd like to learn more about.