Re: A86: 24-bit addressing


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Re: A86: 24-bit addressing



 >On Fri, 5 Sep 1997, Matthew Johnson wrote:
>
>> How does 24-bit addressing work? Odviously it would require three
registers
>> since 8 * 3 = 24, I guess two registers
>> is not enough, from which two registers could only address 65,535 bytes..
I
>> think.
>
>Yes, it requires three registers.  The ROM seems to rely mostly on AHL and
>BDE.  Here are routines that manipulate 24-bit pseudoregisters.
>
>462F _TRANS_AHL_TO_PAGED_AND_SET_PAGE
>4633 _TRANS_AHL_TO_PAGED
>4637 _INC_AHL
>463B _DEC_AHL
>463F _INC_BDE
>4643 _DEC_BDE
>
>Those first two calls translate a 24-bit virtual address into a 16-bit
>physical address.  4633 puts the RAM page in A.  462F goes a step further
>and sets the page for you.
>


Sounds simple enough.  What is the syntax of 24-bit addressing? How do you
convert between 24-bit (virtual?)
addressing and 16-bit physical addressing (by hand) and vise-versa.
 Is the ROM 128K just like the amount of Ram in the 86?
Am I making a mountain out of a mole hill?

One more question.. where do you get these ROM calls from! Jee, you probably
know the 86 better then Pat
does :-)  Do you have some secret archive of rom calls you aren't telling us
about?

Oh and how do you respond so fast! I write a message, and you answer pretty
darn fast!  Have you found a way
to make genetic clones of yourself (with another one of his rom calls!)
........ that would explain alot :-)


- Cyber Optic





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