(I feel a little guilty for bringing up my thread in the exhibition section all the time now...)
So in that case would using parallel loading of latches, help out.?
Already doing that
However, you did give me an idea, even though I use kind of the same principle when reading the keypad buttons. I only read one keypad pr. ISR invocation (when updating a row). This is to save some ISR time. But in the current method I update the same rows on all 6 sides simultaneously.
I'm not sure how much time would be saved if I update a row on only one side at a time, since I use direct port manipulation anyway. But my idea was that I could possibly update one row on side 1, then, the next time the ISR is called, updating the same row on another side, until all 6 sides have the same row updated.
If for nothing else I could call it by some fancy name like, say "hexaphased row display" or something But I would need to increase the ISR frequency for that I think, like maybe 6 times faster. So I'm not too sure about the gain. Then again, it might not be neccessary to have it 6 times faster either, as each row would have its last setting, for all sides that are not updating.
I need to think this through a little more though.
You could use the different colour for am/pm, and a 4x4 is enough to give the full number range.
I like the idea of different colors for am/pm! As for a clock, I should probably have one of those real time modules added. If I could use the normal serial RX/TX for that it would be possible (or else I'm out of pins, but then updating the Cube would be hindred?). But I also think it should be possible without such a module. But then I would have to adjust the time each time I turn it on.
As for 4x4, I made a "nibble font" for use in the cube, so I already have a 4x4 font, with numbers Most characters are actually 3 by 4, leaving 1 column free for separating the characters. Some are 4 by 5, borrowing a row of pixels from the top side. It's pretty minimalistic. I've been meaning to post it for an ordinary 8 by 8 matrix display soon, when I get around to clean it up a bit (Except for the 8x8, I use a 4 by 5 font, so it's slightly bigger - the 4x4 font was a reduction from that one).