common cathode displays are ok for the HT16K33.
I have only checked one common and one digit. That's seems to be OK.
I would do the segment mapping like Adafruit, to have an easier start with a working library.
Usually you would connect the second 4digit display to the same anodes but to a different common.
Regarding 3rd and 4th display - I just wouldn't do it, because most of the libraries will handle the digits per common - and you would need to adopt the library just to use the other anode pins for the different display. I don't say, that's not possible, but imho not worth the efforts.
In your wring above, you have displays attached like this:
1st display: A0-7 and C0-3
2nd display: A8-15 and C4-7
For 2 more displays, use:
3rd display: A0-7 and C4-7
4th display: A8-15 and C0-3
noiasca is probably correct, none of the commonly available libraries will be perfect for driving 16 digits, you may have to use thier functions for driving a 16x8 matrix and write some code to "draw" your digits onto the matrix.
csapsey:
so i'm adding 3rd and 4th displays to the existing C's and A's so it runs them like an LED matrix
Yes. With 2 displays wired as in your original post, you were using 2 quarters of the 16x8 matrix: top-left and bottom-right. The additional 2 displays will become top-right and bottom-left quarters.
