APPENDIX ELEVEN



     4 Stick right (1-4 are four bits of the PIA port)
     5 Potentiometer (paddle) B input (analog pin 1)
     6 Trigger
     7 +5 volts (recommended load of one TTL at 50 ma)
     8 GND
     9 Potentiometer A input (analog pin 2)

     See Creative Computing, August 1983, for an example of using
     the Atari ports for external control.

743,744        2E7,2E8        MEMLO
     It's quite handy to reserve a block of memory below your
     BASIC program and use it to store variables which can be
     passed back and forth between programs with PEEKs and
     POKEs, Here's another routine which will reserve low memory
     for you:

     5 PRINT FRE(0)
     6 REM PROGRAM IS WIPED OUT AFTER RUNNING: B
       E SURE TO SAVE IT FIRST
     7 REM PRINT FRE(0) AFTER RUNNING TO COMPARE
        VALUES
     10 REM REPLACE BYTES VARIABLE WITH NUMBER O
        F BYTES TO PROTECT
     20 MEMLO=BYTES+PEEK(743)+PEEK(744)*256
     30 HIBYTE=INT(MEMLO/256)
     40 LOBYTE=MEMLO-(INT(MEMLO/256)*256)
     50 POKE 743,LOBYTE:POKE 744,HIBYTE
     60 POKE 128,LOBYTE:POKE 129,HIBYTE:REM BASI
        C LOMEM POINTER
     70 POKE 8,0:REM RESET FLAG
     80 X=USR(40960):REM JUMP TO BASIC COLDSTART

752            2F0            CRSINH
     Watch out for conflict with 755 when setting this location (and
     vice versa).

755            2F3            CHACT
     See COMPUTE!'s Third Book of Atari for an article by Frank
     Jones on creating blinking characters.

763            2FB            ATACHR
     Not the color times 16 plus luminance; this is the number of the
     latest COLOR statement, taken from location 200 ($C8). If you
     POKE the number here, BASIC will take the number stored in
     location 200 and dump it, changing your value (not so in ma-
     chine language, however). From Karl Wiegers. Rochester, and
     Judson Pewther, New York.