So to do an 8x8x8 cube the normal way, the minimum digital pin requirement would be 64 for the anodes and another 8 for the cathode/layer drivers. Then we would reload our shift registers and activate the next layer, etc.
Then we would activate one of the eight layers in the cube and turn on the appropriate LEDs in that layer for about 1 ms. We would normally build an 8x8x8 cube by bringing 64 anodes down to the main board, where they would be configured by a bunch of shift registers.
