641



641            281            PTRIG5

642            282            PTRIG6

643            283            PTRIG7

644            284            STRIG0
     Stick trigger 0. This and the next three locations perform the
     same function as the PTRIG locations except for the joysticks.
     Like PTBIG, zero is returned when the button is pressed; one is
     returned when it is not. STRIG registers are shadow registers for
     GTIA/CTIA locations 53264 to 53267 ($D010 to $D013).

645            285            STRIG1

646            286            STRIG2

647            287            STRIG3

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Locations 648 to 655 ($288 to $28F) are for miscellaneous OS use.

648            288            CSTAT
     Cassette status register.

649            289            WMODE
     Register to store either the read or the write mode for the cassette
     handler, depending on the operation: zero equals read, 128 ($80)
     equals write.

650            28A            BLIM
     Cassette data record buffer size; contains the number of active
     data bytes in the cassette buffer for the record being read or
     written, at location 1021 ($3FD). Values range from zero to 128
     (cassette record size is 128; $80). The pointer to the byte being
     read or written is at 61 ($3D). The value of BLIM is drawn from
     the control bytes that precede every cassette record, as
     explained in location 1021.

651-655        28B-28F        ....
     Spare bytes. It is not recommended that you use the spare bytes
     for your own program use. In later upgrades of the OS, these
     bytes may be used, causing a conflict with your program. For
     example, the new OS ROMs use locations 652 and 653 ($28C,
     $28D) in the new IRQ interrupt handler routines. It is best to use a
     protected area of memory such as page six, locations 1536 to
     1791 ($600 to $6FF).

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Locations 656 to 703 ($290 to $2BF) are used for the screen RAM
display handler (depending on GRAPHICS mode).