17



      5       32     The serial input data ready interrupt is
                     enabled.
      4       16     The serial output data required interrupt is
                     enabled.
      3        8     The serial out transmission finished
                     interrupt is enabled.
      2        4     The POKEY timer four interrupt is enabled
                     (only in the "B" or later versions of the OS
                     ROMs).
      1        2     The POKEY timer two interrupt is enabled.
      0        1     The POKEY timer one interrupt is enabled.

     Timer interrupt enable means the associated AUDF registers are
     used as timers and will generate an interrupt request when they
     have counted down to zero. See locations 528 to 535 ($210 to
     $217) and the POKEY chip from locations 53760 ($D200) on, for a
     full explanation. 192 ($C0) is the default on powerup.

     You can also disable the BREAK key by POKEing here with 64
     ($40; or any number less than 128; $80) and also in location
     53774. The problem with simple POKEs is that the BREAK key is
     re-enabled when RESET is pressed and by the first PRINT
     statement that displays to the screen, or any OPEN statement that
     addresses the screen (S: or E:), or the first PRINT statement after
     such an OPEN and any GRAPHICS command. In order to
     continually disable the BREAK key if such commands are being
     used, it's best to use a subroutine that checks the enable bits
     frequently during input and output operations, and POKEs a
     value less than 128 into the proper locations, such as:

     1000   BREAK = PEEK(16) - 128: IF BREA
            K < 0 THEN RETURN
     1010   POKE 16, BREAK: POKE 53774, BRE
            AK: RETURN

     The new OS "B" version ROMs have a vector for the BREAK key
     interrupt, which allows users to write their own routines to
     process the interrupt in the desired manner. It is located at 566,
     567 ($236, $237).

17             11             BRKKEY
     Zero means the BREAK key is pressed; any other number means
     it's not. A BREAK during I/O returns 128 ($80). Monitored by
     both keyboard, display, cassette and screen handlers. See
     location 16 ($A) for hints on disabling the BREAK key. The latest
     editions of OS provide for a proper vector for BREAK interrupts.
     The BREAK key abort status code is stored in STATUS (48; $30).
     It is also checked during all I/O and scroll/draw routines. During
     the keyboard handler routine, the status code is stored in DSTAT