Create grid like background inside multiline textbox

Question

I have a very un-usual requirement regarding textbox.
1. I need a multiline-textbox of 5 Lines, with each line of 22 characters.
2. The textbox should have grid like background (with rows & columns lines) & each cell should have only one character. This means there will be five rows & each row should have 22 cell/boxes & each box should contain only one character.
Please advise! I have no clue how to do this. I did a lot of google, but no results.