Re: Apple II weather display

[Michael J. Mahon <mjmahon@aol.com>]

BLuRry <brendan.robert@gmail.com> wrote:
> On Apr 20, 7:12 pm, Osgeld <osg...@cheesefactory.us> wrote:
>> I dont even know where to begin with ASM, any good references for the
>> total noob? especially for the apple but generic would function as well
> 
> Everything you ever wanted to know about 6502 assembler:
> http://6502.org/
> 
> Just a few basic rules to help frame things for you:
> The CPU has only three registers that can hold values: A[ccumulator],
> X and Y.  Most of the operations you can perform will be in the
> accumulator.  The 6502 also has opcode variants to speed things up for
> memory locations in the first 256 bytes of ram, called the "Zero
> Page".  So you could use memory locations in the zero page (sometimes
> affectionately abbreviated ZP) for additional variable storage, just
> try not to clobber anything in use by [Pro]DOS if you're trying to
> peacefully co-exist with a resident OS.
> 
> There's lots of great articles in Nibble magazines (that's where I
> learned):
> http://www.nibblemagazine.net/
> 
> And to code assembler you'll need... well... an assembler of course!
> 6502.org has an exhaustive list (though quite dated) here:
> http://www.6502.org/tools/asm/
> My favorite has been Acme for some time:
> http://www.esw-heim.tu-clausthal.de/~marco/smorbrod/acme/
> Though if you want to be totally hard-core old school then you could
> use an assembler on the machine directly like Merlin or ORCA/M.
> Personally I find it easier to cross-assemble and send programs over
> to an emulator for testing.  Then send via serial for final testing on
> real hardware later.
> 
> I suppose this topic should be a new subject line.  Oh well, such is
> life.  This message board is dripping with 6502 coding veterans (and
> junkies alike).  Just ask and we'll help!

I'd just re-spin page zero some...

Indirect addressing through page zero is really the only method for
addressing variable addresses.  As a result, page zero can also be thought
of as a bank of 128 address registers!

If your software runs cooperatively with other software--like AppleSoft or
ProDOS--then it is handy to restrict your use of page zero to those
locations they leave unused (to avoid having to save and restore it at each
transition). 

-michael  -  NadaNet 3.1:  http://home.comcast.net/~mjmahon