On the ATARI 1200XL there are 4 function keys named F1 to F4

Function Keyproduces
F1 Cursor up
F2 Cursor down
F3 Cursor left
F4 Cursor right
Shift F1 Cursor Home
Shift F2 Cursor End
Shift F3 Cursor to beginning of line
Shift F4 Cursor to end of line
CTRL F1 toggles Keyboard enable/disable
CTRL F2 toggles DMA enable/disable
CTRL F3 toggles Key-Click
CTRL F4 toggles Standard/International character set
Shift CTRL F1 ignored
Shift CTRL F2 ignored
Shift CTRL F3 ignored
Shift CTRL F4 ignored

see also: Keyboard_topics