65528



     locations 520, 521 ($208, $209) to 65470 ($FFBE). This is the
     keyboard service routine. It processes debounce, and SHIFT-
     CTRL logic (see location 559; $22F); saves the internal keyboard
     code in 754 ($2F2) and 764 ($2FC); sets the ATTRACT mode flag
     at 77 ($4D) and sets location 555 ($22B -- SRTIMR) to 48 ($30).

65528          FFF8           CHKSUN
     According to Softside Magazine, December 1981, if a PEEK here
     returns 255, then you have the older OS ROM(s). There were
     some troubles with cassette loads in the older ROMs that
     sometimes require the following to cure:

     Do an LPRINT without a printer attached before CLOAD. This
     clears the cassette buffer.

     Press RESET before CSAVEing or CLOADing will restore the
     system to its initialization parameters and help with loading and
     saving routines.

     There is a new OS available from Atari which fixes a bug that
     would cause the I/O operations to "time out" for a few seconds. It
     apparently does not alter any of the routines mentioned here.

     The chip reset interrupt (powerup) vectors through location
     65532 ($FFFC) to 58487 ($E477) where a JMP vector to the
     powerup routine is located. A chip reset is not the same as
     pressing the RESET key, which in itself does not generate a chip
     reset.

     The NMI interrupts are vectored through 65530 ($FFFA) to the
     NMI service routine (ISR) at 59316 ($E7B4), and all IRQ
     interrupts are vectored through 65534 ($FFFE) to the IRQ service
     routine at 59123 ($E6F3). In these service routine areas, the
     cause of the interrupt is determined, and the appropriate action
     is taken, either by the OS or through a JMP to a RAM vector
     where a user routine exists.