Re: Does an enhanced //e _ALWAYS_ have 80 col. support?

[mjmahon@aol.com (Michael J. Mahon)]

Craig Bower \(Bender MX\) wrote:

>"Don Bruder" <dakidd@sonic.net> wrote in message 
>news:D0Lod.7227$_3.88700@typhoon.sonic.net...
>> ERROR! ERROR! ERROR! ERROR!!!
>>
>> When playing with soft-switches, *ALWAYS* *READ* from them, unless
>> specifically told that writing to activate them is OK. Some of them
>> don't care. Others will toggle twice when written. (A read involves one
>> access, a write involves two accesses - one to "locate" the address, the
>> second to do the actual write)
>
>Hi Don,
>
>Excellent point!! - I just assumed that since a poke command will have to
>"read from" before it "writes to" a location, that a STA would be ok.
>
>The best bet is to try it with a scrap floppy (or scrap emulator image!)
>and test what works!
>
>Thanks for the pick-up Don!

Nope, it's incorrect, as explained in my reply to Don's post.

And there is nothing logical about assuming that POKE will
read before writing a location--it's just an artifact of the 6502
microarchitecture.

In fact, the 65C02 does not access the store location twice
for an absolute, indexed STORE, unless there is no page
crossing as a result of the indexing!

-michael

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