Re: A86: can one program be on two pages?
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Re: A86: can one program be on two pages?
Don't forget that they used the z80 because it IS an 85 compatible
calculator, even on the assembly level. They would have had to rewrite the
entire rom if they used a 68k. But I agree, paged memory can really be a
lot of trouble.
At 10:16 AM 6/24/98 -0400, you wrote:
>
>Hi,
>
>Once again I'm going to annoy you all with my lame newbie questions..
>but seeing as how the TI-86 uses a paged RAM (as well as ROM, of
>course) system, isn't it possible to have programs start on, say,
>page 2 and overflow into page 3? In theory I could load page 2
>into the low 16k and page 3 into the high 16k - that would
>accomodate programs up to 32k (in theory). Is there a ROM call to do
>this? If not, does the byte receive code in the ROM check after
>-every byte- to see if its overflowed the current RAM page and in
>that case swap in a new page? I know I can use _load_ram_ahl to
>automatically swap in the RAM page where a program begins... but
>what happens if the program is bigger than 16k? Is there a limit
>on the calc of 16k, 32k, or none at all? If programs can be more than
>32k (and I believe somebody said they can be up to 64k) then the
>calc has to do some checking in link routines as to whether or not
>it needs to swap onto a new page. This could potentially get very
>messy... I'd need some kind of routine to convert between an absolute
>address and a RAM page/hl combo (like _load_ram_ahl)
>
>For reading (I.E. sending to the E2) I suppose I could use the
>_get_word_ahl call (which returns a word pointed to by ahl in
>de, if I recall) instead of a simple ld a,(hl) or whatever. That would
>mean I could just do a 24 bit inc on ahl and handle files as large as
>the entire memory. But what about writing (I.E. receiving from the E2)?
>Will I need to write a kind of _put_word_ahl?
>
>Is it just a matter of calling _load_ram_ahl after every single byte
>and inc'ing ahl between bytes? That may work on both send and
>receive, but it seems awefully slow. Swapping RAM pages must take
>quite a few CPU cycles. Will _load_ram_ahl still swap pages if the
>right page is already swapped in?
>
>I think TI really bombed on this paged memory thing. If it can't
>be done easily with a z80, its time to find another processor. They
>could have spent another $2 and put a 68k into the damn thing...
>I think they finally got a clue with the TI-89. Don't get me wrong,
>there are a lot of very dedicated and intelligent z80 people who
>swear by the chip... but they've created a real programming mess with
>paged RAM.
>
>Thanks for all your help, this list is an awesome resource.
>
>--
>Bryan Rittmeyer
>mailto:bryanr@flash.net
>http://www.bridges.edu/horizon/
>
>
// David Phillips
// mailto:electrum@tfs.net
// ICQ: 13811951
// AIM: electrum32
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