Re: Possible IIc Hardware Problems (also Re: Modem for Apple IIc)

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <55u65v$28q@news.emi.com> drsmooth@relex.com writes:
>[...]
>Does your program even *get* to the error trapping routine?  Maybe you
>need to use this wierd routine that I found in the Applesoft ][
>manual?  (If anyone knows what this routine is, and what it does, I'd
>love to know; it is mostly a buncha POKEs, and it says it is to be
>used when encountering 43+ errors.)

What those pokes do is set up a short machine-language subroutine that
fixes the 6502 stack after an error occurs.  The Applesoft error handler
has a bug in it--it often leaves extraneous junk on the stack, which has
a number of bad side effects:  the RETURN statement can't find its
corresonding GOSUB anymore (since GOSUB/RETURN uses the stack to remember
where to return to), the NEXT statement can't find its corresonding FOR,
etc.

CALLing that machine-language routine from inside your ONERR GOTO routine
removes the extraneous junk from the stack, curing the above problems.

               - Neil Parker
-- 
Neil Parker, nparker@{cie-2,cie}.uoregon.edu, http://cie-2.uoregon.edu/~nparker

                     "Bad move, Neil!"  -- The Tick