So, there are some tricky bits to serial communications that I feel it would be good to share.

First oddity: The computer sends a CR character (decimal 13) when the user pushes Enter, but the ATmega must send a CR(13) and an LF(10) character to move the cursor to the beginning of the next line.

Second oddity: Backspace does not delete the character. It will only move the cursor back one. So, to erase a character, you must send a backspace character (decimal 127), then a space(32) to clear the old character, and then a backspace to move the cursor back again.

That's it for simple stuff. Now for escape sequences! ANSI escape sequences are mystical combinations of characters that carry special meaning. Generally, they all start with the ascii ESC character (decimal 27), followed by the left square bracket (decimal 91). After this sequence of characters, which is called the Control Sequence Introducer, you will find any number of other characters that indicate which control sequence it is. It's so much fun, I can hear you scream with joy already.

Here are a list of examples of commands that the ATmega can send to the terminal, all of which begin with ESC [

• Moving the cursor around, relative to its current position
  • A - move the cursor one space up
  • B - move the cursor one space down
  • C - move the cursor one space forward
  • D - move the cursor one space back
  • 5C - move the cursor 5 spaces forward. A-D can all have numbers before the letter to indicate how far to move the cursor
• Move the cursor to an absolute position
  • 10G - move the cursor to the 10th column. The 1st column is the left-most column
  • 2;3H - move the cursor to the 2nd row and the 3rd column
  • 2;3f - another way of moving the cursor to the 2nd row and the 3rd column
• Clear parts of the screen
  • 0J - Clear from the cursor to the end of the screen
  • 1J - Clear from the cursor to the beginning of the screen
  • 2J - Clear the entire screen, and optionally move the cursor to the upperleft corner, depending on the terminal
  • 0K - Clear the rest of the line after the cursor
  • 1K - Clear from the beginning of the line to the cursor
  • 2K - Clear the entire line, doesn't move the cursor

Of course, the terminal doesn't like being bossed around, so it often talks back to the ATmega, with the following commands that also start with ESC [. They usually come from special keys that have been pushed, but they don't do anything until the ATmega gives the commands to actually move the cursor.

• Arrow keys
  • A - up arrow
  • B - down arrow
  • C - right arrow
  • D - left arrow
• Other exciting keys
  • 2~ - the insert key
  • 3~ - the delete key
  • 1~ - the home key
  • 4~ - the end key
  • 5~ - page up
  • 6~ - page down

Other input notes:

• Control - Holding the control key while pushing a letter will present as the ASCII code of the lowercase letter, minus 96. For example, S has a lowercase ASCII value of 115, so Ctrl+S is 19. Holding Shift or having Caps on while pressing Control will not effect this, it will still be 96 less than the lowercase ASCII value.
• Alt - Holding the alt key while pushing a character will present as the ESCAPE key (decimal 27), followed by the ascii code of the letter. This values will be different based on the Caps lock status. Holding Shift and Alt while pressing a character will not send anything.
• Control & Alt - It will send the ESCAPE character, followed by the character than is 96 less than the lowercase ASCII value of the letter that was pressed.

Additional information about ANSI: Wikipedia