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Anyone know how the BASIC ROM works?

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  • spirantho
    Hi everybody, My Tutor emulator is faring quite nicely - I now have the graphic editor working fine (at last) but am quite stumped when going into the BASIC
    Message 1 of 2 , Apr 16, 2003
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      Hi everybody,




      My Tutor emulator is faring quite nicely - I now have the graphic
      editor working fine (at last) but am quite stumped when going into the
      BASIC ROM.




      Assuming the ROM dump I have is correct (and it seems ok), there is a
      routine which takes commands from R11 (the program counter after
      calling the routine in other words) and then parameters if necessary
      from after that. The routine then appears to do various things
      according to the command before looping back round again. The loop
      appears to be begin at >5380.


      The problem is the "command" with the value F322 - it seems invalid,
      but it appears in a place which looks good (directly after a valid
      command) and is repeated with a different operand. The problem is that
      the routine takes a jump address from the (command & >01e0) >> 5 added
      to a lookup table at >584c. This would be great but F322 & 01E0 = 0110
      and 0110 >> 5 is 3 - which is ODD! Not surprisingly this jumps
      merrily into the location straddling two routines in the lookup table,
      and gets lost by jumping to >6855.




      Does anyone here have any idea what's going on? Has anybody tried to
      understand the ROM before me? I've got a pretty good idea about how
      most of it works now, but I can`t figure this out yet.




      Thanks for any help! If anyone wants I can send them my source code
      to have a look at...




      Ian Gledhill


      IanG@... avatar@...
    • emucompboy
      Sure, send it along and I ll look at it and steal it! It s what I do best! Ha ha ha ha ha! emucompboy ATnospam yahoo DOTnospam COMnospam ... code
      Message 2 of 2 , Apr 21, 2003
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        Sure, send it along and I'll look at it and steal it! It's what I do
        best! Ha ha ha ha ha!

        emucompboy ATnospam yahoo DOTnospam COMnospam


        --- In tomytutor@yahoogroups.com, "spirantho" <IanG@a...> wrote:

        > Thanks for any help! If anyone wants I can send them my source
        code
        > to have a look at...
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