Re: 6502 illegal opcodes questions

[pausch@saaf.se (Paul Schlyter)]

In article <S6mdnYNMG-caHhnZnZ2dnUVZ_vidnZ2d@comcast.com>,
Michael J. Mahon <mjmahon@aol.com> wrote:

> Paul Schlyter wrote:
> 
>> Some programming languages even had these formatting rules built-in.
>> In e.g. FORTRAN (up to FORTRAN-77), these rules had to be obeyed:
>> 
>> Column 1:      C or * marked the whole line as a comment
>> Columns 2-6:   Labels went here - 1-5 decimal digits
>> Column 7:      A non-space character here marked this line as a contination line
>> Columns 8-71:  The program statement went here
>> Columns 72-80: Comment - anything here was ignored by the compiler
> 
> Actually, it was:
> 
> Column 1-5:    Statement number, or "C" in column 1 for comment lines
> Column 6:      Non-blank marks continuation line (often 1-9 to indicate
>                 sequence of the continuations if more than one)
> Columns 7-72:  FORTRAN Statement
> Columns 73-80: ID/sequence field, ignored by compiler

Thanks for the correction.  Yep, my fortran skills are getting rusty -- it's some
20 years since I last coded in that language.

 
> The sequence field was often left blank on manually keypunched cards,
> but was almost always filled with some combination of a "deck" ID and
> a sequence number on machine-punched decks, as were "binary" decks.
> 
> I remember many times using an IBM 82 card sorter to restore order
> to a deck containing gravity-induced entropy.  ;-)
> 
> There is an interesting historical reason for the FORTRAN compiler
> to ignore columns 73-80.  FORTRAN was first implemented on the IBM 704
> computer, and that machine and its successors, the 709, 7090, 7040,
> and 7094, all used a binary card console card reader that read in
> "row binary".  Since these machines had 36-bit words, the standard
> binary card format was 12 pairs of 36-bit words, read from successive
> rows of the card, and therefore covering only the first 72 columns.
> 
> As a result, the computer could not read columns 73-80 from the console
> card reader, and those columns were already conventionally used for
> deck sequence numbers.  FORTRAN merely continued that convention.
> And, of course, what the computer could not read, the compiler must
> ignore.  ;-)
> 
> For example, see:
> 
> www.atkielski.com/PDF/data/fortran.pdf
> 
> -michael
> 
> Parallel computing for 8-bit Apple II's!
> Home page:  http://members.aol.com/MJMahon/
> 
> "The wastebasket is our most important design
> tool--and it is seriously underused."
> 
> 
> 
> 
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