765



     keyboard).

     When a read request is issued to the keyboard, CH is set to 255
     by the handler routine. After a keycode has been read from this
     register, it is reset to 255. BREAK doesn't show here, and CTRL
     and SHIFT will not show here on their own. However, the inverse
     toggle (Atari logo key), CAPS/LOWR, TAB and the ESC keys
     will show by themselves. You can examine this register with:

     10 LOOK=PEEK(764)
     20 PRINT "KEY PRESSED = ";LOOK
     30 POKE 764,255
     40 FOR LOOP=1 TO 250:NEXT LOOP
     50 GOTO 10

     See COMPUTE!'s First Book of Atari for an example of using this
     register as a replacement for joystick input.

765            2FD            FILDAT
     Color data for the fill region in the XIO FILL command.

766       2FE       DSPFLG
     Display flag, used in displaying the control codes not associated
     with an ESC character (see location 674; $2A2). If zero is
     returned or POKEd here, then the ATASCII codes 27 - 31, 123 -
     127, 187 - 191 and 251 - 255 perform their normal display screen
     control functions (i.e., clear screen, cursor movement,
     delete/insert line, etc.). If any other number is returned, then a
     control character is displayed (as in pressing the ESC key with
     CTRL-CLEAR for a graphic representation of a screen clear).
     POKEing any positive number here will force the display instead
     of the control code action. There is, however, a small bug, not
     associated with location 766, in Atari BASIC: a PRINTed CTRL-R
     or CTRL-U are both treated as a semicolon.

767            2FF            SSFLAG
     Start/stop display screen flag, used to stop the scrolling of the
     screen during a DRAW or graphics routine, a LISTing or a
     PRINTing. When the value is zero, the screen output is not
     stopped. When the value is 255 ($FF; the one's complement), the
     output to the screen is stopped, and the machine waits for the
     value to become zero again before continuing with the scrolling
     display. Normally SSFLAG is toggled by the user during these
     operations by pressing the CTRL-1 keys combination to both start
     and stop the scroll. Set to zero by RESET and powerup.

---------------------------------------------------------------------------
PAGE THREE
Locations 768 to 831 ($300 to $33F) are used for the device handler and
vectors to the handler routines (devices S:, P:, E:, D:, C:, R: and K:).