I don't know if this is possible, but I'd like to basically tell a group of
cells how many characters it's allowed to have (one in this case), and after
I've entered the character, I'd like to automatically be moved to the next
cell without having to actually hit ENTER.

I need to enter about 600 1s and 2s, one number per cell, and as you can
imagine, hitting ENTER each time can become quite tedious.

Thanks in advance!