I think I may be going down the wrong road here - I need to drive a simple cube of LEDs (I know, that was something done 2-3 years ago - what can I say, i'm slow). I have 16 input, and 4 common leads. Very simple - just need to multiplex on the common.
The issue I have is finding led-driver chips. Right now I'm driving it from an Arduino Nano and some OLD 74HC595 and it's just too slow or rather, since I have to use the Arduino to constantly multiplex it just cannot keep up with updates, multi-plexing etc. so I think I need to use an LED driver where simple flipflops and a on-chip multiplex will allow the processor to just deal with sending updates.
The MAX7912 and my old AS1108 all are 8 bit and initially I wrongly assumed I just would use two of them to get 16 bits, but I cannot share the common leads this way. And that's where I am running into a wall. Searching Digikey I can easily find drivers for 16 pins or a lot more, but what I cannot find a way to do is specify the number of common pins. So I think I'm hunting for a dumb and uncommon solution. If I separate the commons so each driver chip would have it's own, I would loose the stability of the cube design as it stands right now - I don't want to treat the cube as I would a set of 7 segment displays that are all isolated. The idea is to control the multiplexer across the whole cube not treating it as several small devices put together. The old designs out there seem to share this idea too.
Since my cube is very small I didn't expect there to be a need for a lot of chips. Well, since I'm not using the driver right now I have plenty of transistors - another reason I am looking for a LED driver instead.
My hope is that there are drivers with more common leads too. Or is the solution to use 4 chips like STP16CPC26 and use the controller to multiplex between them? It seems it's only half a driver since it doesn't deal with the multiplexing at all.
So I'm a bit lost about the right approach here. I had hoped that I could get two AS1108 going, very simple - but they cannot share the common leads (that I know of). So what's a better approach? Note, this is again a learning project. Besides the multi-plexing i'm also looking to get my current requirements right on this. So I really am not looking for "follow this instructable" - I am hoping to come away from this crazy simple project a little more knowledgeable.