Groups > comp.sys.apple2.programmer > #5928

Re: Woz learns assembly language

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From	awanderin <awanderin@gmail.com>
Newsgroups	comp.sys.apple2.programmer
Subject	Re: Woz learns assembly language
Date	Thu, 16 Dec 2021 00:41:41 -0700
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D Finnigan <dog_cow@macgui.com> writes:

> Has anyone ever thought about how Woz learned 6502 assembly language for the
> Apple I and Apple II? I have wondered it a few times when I look at Monitor
> source and think about the integer BASIC that he wrote. How long did it take
> him to learn 6502 and become proficient enough to write Monitor, BASIC, and
> other utilities for the Apple? Did Woz know assembly for another CPU?
>
> 6502 was a fairly new CPU, and even though based on the earlier Motorola
> 6800, neither one had been out for more than a few years by the time the
> Apple I and II were introduced in '76 and '77.
>
> He had others around to help him, at least to the extent of answering his
> questions or loaning him technical docs; this is certain.
>
> Anyone know more about how Woz learned to program the 6502?

No idea how Woz learned 6502, but I'll guess.

Woz says that he designed many computers before he actually built the
Apple I.  He talked about how he obsessed over things, like how many
chips in a design.  I suspect he also obsessed over the details in data
books and manuals for computers.  He basically crammed his mind full of
every detail he could find.

I would bet he probably studied the opcodes, and constantly thought
about the result he wanted to achieve.  His intense concentration and
his subconscious probably helped a ton.

One example is the binary-to-decimal converter he wrote.  I cannot find
it right now, but I recall he used shifts (ASL) with BCD-mode (SED), and
came up with a pretty clever way to convert a number for printing.
It seems like he tried to think of every possible way to use the
different 6502 instructions.  Maybe, that's how he came up with this
stuff?

The other thing is, he had already built many electronic devices, and
understood digital logic circuits really well.  When he looked at the
6502 data book, he probably figured out how it worked inside.  It might
have not been too much more effort for him to put those opcodes to use.

-- 
--
Jerry    awanderin at gmail dot com

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