Print-screen key (INT 05h)

        Automatically called by keyboard scan when print-screen key
        is pressed. Normally executes routine to print the screen, but
        may call any routine that can safely be executed from inside
        the keyboard scanner. Status and result byte for default handler
        is at address 0050:0000.

                Status byte at 0050:0000
                00  Print-screen not active (never executed,
                    or last call was successfull).
                01  Print-screen in progress.
                FF  Print-screen not active - last call caused some sort
                    of error. Cleared by next call to print-screen.