54017



     Left     = BIT 2,6 = 1
     Right    = BIT 3,7 = 1
     Neutral  = All four jack bits = 1

     PORTA is also used to test if the paddle 0-3 triggers (PTRIG) have
     been pressed, using these bits:

     Bit       7     6     5     4     3     2     1     0
     PTRIG     3     2     -     -     1     0     -     -

     Where zero in the appropriate bit equals trigger pressed, one
     equals trigger not pressed.

     The PORT registers are also used in the keyboard controller (used
     with a keypad) operation where:

     Bit       7     6     5     4     3     2     1     0
     Row       4     3     2    Top    4     3     2    Top
     Jack     ..........2..........   ..........1...........

     Columns for the keyboard operation are read through the POT
     (PADDL) and TRIG registers. See Micro, May 1982, and the
     Hardware Manual for more information on jacks and ports.

54017          D301           PORTB
     (W/R) Port B. Reads or writes data to and/or from jacks three and
     four. Same as PORTA, above, for the respective jacks. Shadow
     registers are: STICK2 (634; $27A, jack three), STICK3 (635, $27B,
     jack four), and PTRIG4-7 (640-643; $280-$283).

54018          D302           PACTL
     (W/R) Port A controller (see 54016 above). POKE with 60 ($3C) to
     turn the cassette motor off, POKE with 52 to turn it on. You can put
     a music cassette in your program recorder, press PLAY and then
     POKE 54018,52. Your music will play through the TV speaker or
     external amplifier while you work at the Atari. You can use this
     technique to add voice tracks to your programs. To turn off the
     music or voice, type POKE 54018,60.

     PACTL can be used for other external applications by the user. Bit
     use is as follows:

     Bit             Function
     7 (read only)   Peripheral A interrupt (IRQ) status bit. Set by
                     Peripheral (PORT) A. Reset by reading PORTA
                     (53774; $D20E).
     6               Set to zero.
     5               Set to one.
     4               Set to one.
     3 (write)       Peripheral motor control line (turn the cassette on
                     or off; zero equals on).
     2 (write)       Controls PORTA addressing. One equals PORTA