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   REPLYADDR gh424NO584SPAM@cox.net   
   REPLYTO 3:770/3.0 UUCP   
   MSGID: <20211114-040302.878.0@George.ssl-us.astraweb.com> 1cb1e1cc   
   PID: SoupGate-Win32 v1.05   
   I was going over some of my old CBM files from back in the day, and ran   
   across an error I had found in the Plus 4 kernel rom.  I don't think I ever   
   found a way to report it to anyone, so I thought I would see if anything   
   has changed.   
      
   The error is in the 6551 ACIA servicing routine where a byte is read in   
   from the ACIA:   
      
   LDA $FD00   
   BEQ EAC2   
   STA $07D5   
      
   Incoming bytes are first stored at $0FD5, and later moved from there into   
   the input buffer.  But as the rom is written, any null byte (00) received   
   would be later stored as whatever the most recent non-null byte was.  And   
   it's impossible to receive a null byte.  The solution is to reverse the   
   second and third instructions:   
      
   LDA $FD00   
   STA $07D5   
   BEQ EAC2   
      
   Or you could duplicate the beginning of the IRQ servicing up to this point   
   in your code, with the correction, then jump back into the rom.   
      
   Of course, this being the Plus 4, it may be that nobody would ever care   
   about this, but it would be nice to make a record in case anyone ever   
   wanted to make other revisions to the ROM, or actually make use of the UART   
   capability of the Plus 4.   
      
   George Hug   
   --- SoupGate-Win32 v1.05   
    * Origin: Agency HUB, Dunedin - New Zealand | Fido<>Usenet Gateway (3:770/3)   
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