53277



     4        16     Player 0
     3         8     Missile 3
     2         4     Missile 2
     1         2     Missile 1
     0         1     Missile 0

53277          D01D           GRACTL
     (W) Used with DMACTL (location 54272; $D400) to latch all stick
     and paddle triggers (to remember if triggers on joysticks or
     paddles have been pressed), to turn on players and to turn on
     missiles. To get the values to be POKEd here, add the following
     options together for the desired function:

                             Decimal   Bit
     To turn on missiles        1       0
     To turn on players         2       1
     To latch trigger inputs    4       2

     To revoke P/M authorization and turn off both players and
     missiles, POKE 53277,0. Once latched, triggers will give a
     continuous "button pressed" read the first time they are pressed
     until BIT 2 is restored to zero. Triggers are placed in "latched"
     mode when each individual trigger is pressed, but you cannot set
     the latch mode for individual triggers.

     Have you ever hit BREAK during a program and still had players
     or their residue left on the screen? Sometimes hitting RESET
     doesn't clear this material from the screen. There are ways to get
     rid of it:

     POKE 623,4: This moves all players behind playfields.
     POKE 53277,0: This should turn them off.
     POKE 559,2: This should return you to a blank screen.

     Make sure you SAVE your program before POKEing, just in
     case!

53278          D01E           HITCLR
     (W) POKE with any number to clear all player/missile collision
     registers. It is important to clear this register often in a program
     -- such as a game -- which frequently tests for collisions.
     Otherwise, old collision values may remain and confuse the
     program. A good way to do this is to POKE HITCLR just before
     an event which may lead to a collision; for example, right before
     a joystick or paddle is "read" to move a player or fire a missile.
     Then test for a collision immediately after the action has taken
     place. Remember that multiple collisions cause sums of the
     collision values to be written to the collision registers; if you do
     not clear HITCLR often enough, a program checking for
     individual collisions will be thrown off by these sums.