I'm trying to build a LED matrix with 5 MAX 7221, I started of course with one Drive 7221 to understand how it works, but I'm having problems.
The first, which is rather strange, is that what little works, it works by connecting the DIN dell'arduino to pin 24 of the MAX 7221, but that is the DOUT, ??because if I connect the Arduino DATAIN to PIN 1 of 7221, nothing happens .
The other problem is that everything seems to work fine, up to a maximum of three rows of LEDs connected, just plug in the 4, strange things happen, the three previous files turn off and turn on only the last connected, but in the opposite direction, that is, before they lit three vertical rows, attacking the fourth, you turn on only the horizontal.
Someone can give me some help.
I redid all the connections again, on another breadboard, and now everything works like a charm