ROM Computer Magazine Archive ROM MAGAZINE ISSUE 2 — OCTOBER/NOVEMBER 1983 / PAGE 13

Yellow Brick Road by
Peter Ellison

    In the last issue of ROM I showed how one can use the keyboard for input by PEEKing into the Atari's memory. In this issue I'm going to show you how easy it is to use the Console keys (The three yellow keys at the right side of the terminal). These keys are very useful for games, business programs, or whatever different selections need to be made. To set up this program we must first PEEK into the memory at 53279 decimal. This checks to see what special purpose key is being pressed. Below is a table that shows if PEEK(532779) equals that number then that key is being pressed.

Table 1
  7=no key pressed
  6=START key pressed
  5=SELECT key pressed
  4=SELECT and START keys pressed
  3=OPTION key pressed
  2=OPTION and SELECT keys pressed
  1=OPTION and SELECT keys pressed
  0=OPTION, SELECT, and START pressed

    The program below checks to see what key is being pressed and then prints out what is being pressed.

  10 A=PEEK(53279)

  20 ON A+1 GOTO 25,30,35,40,45,50,55,60
  30 ? "OPTION, SELECT    ":GOTO 10
  35 ? "OPTION, START    ":GOTO 10
  40 ? "OPTION         ":GOTO 10
  45 ? "SELECT, START    ":GOTO 10
  50 ? "SELECT    ":GOTO 10
  55 ? "START    ":GOTO 10
  60 ? "NONE     ":GOTO 10

    Remember next time you make a game or program that requires. changing a level or number of players use the special purpose keys, their easy to use.
    The second thing that will be discussed in this section is, "The Cursor". Yes, the little white thing that flashes on and off while you're typing in programs. This cursor can change color, blink, move, be positioned, and a whole lot more. Just by poking a number, each of these things can be done. For instance by typing POKE 752,1 you can turn the cursor completely off. Below is a Table that shows the different things that can be done with the cursor.

            The Cursor
LMARGIN    82    Left Margin
RMARGIN    83    Right Margin
ROWCRS     84    Cursor Row
COLCRS     85    TAB
TXTROW    656    Cursor Row
TXTCOL    657    Cursor Column
CHACT     755    4=Vert, 2=Norm, 1=Blank
CRSINH    752    0=ON, 1=OFF
COLOR1    709    Color of Cursor

    As you can see from the table above the cursor can be made to do just about anything by poking the right locations. The color of the cursor can be made lighter or darker by typing in POKE 709,X where X=0-255. Also by typing in POKE 755,4 all of the written text is displayed upside down. The cursor is a useful thing in programming when one knows how to use it. In the next issue of 'The Yellow Brick Road', player/missile graphics will be discussed with all of the locations needed to use them.

Yellow Brick Road