[Coco] Cartridge memory - mapping in and out

Roger Taylor operator at coco3.com
Wed Oct 31 21:54:54 EDT 2007

At 08:23 AM 10/30/2007, you wrote:
>Quoting Arthur Flexser <flexser at fiu.edu>:
>>P.S.  I should have elaborated that a bit more....Super Extended
>>Basic is very cleverly patched into the CoCo 1/2 Basic in such a way
>>as to allow going to ROM mode without anything weird happening.  All
>>the hooks into the Super Extended code have "underneath" them, in
>>ROM, the standard, un-Super vectors,  so all that happens when you
>>switch out Super Extended Basic by going to ROM mode is that you
>>revert to the CoCo 1/2 version of Basic, pretty much.  Same thing if
>>you copy ROM to RAM.  If you try to reference a Super Ext. Basic
>>command, you just get a syntax error, not a crash, same as if you
>>tried that on a CoCo 1/2.
>Humm this has got me thinking so what where the extra facilities
>offered by SECB ?
>where these all commands and functions designed to handle the new
>graphics moades and other hardware of the CoCo3 or is there stuff in
>there that would be of use
>to a CoCo 1/2 etc.
>The reason I ask is that it should be possible to backport SECB to any
>CoCo running in all RAM mode, asuming that there is something usefull
>to backport :)

SECB uses the MMU a lot and accesses memory outside of the 64k 
address space, not available on anything but the CoCo 3.

>Also when accessing DOS I presume that it would switch to using the
>DOS ROM on the DOS cart for that or did the extra SECB code reside in
>the $E000-$FEFF area where it would not normally interfere with a copy
>of the DOS rom in the $C000-$DFFF area ?

No switching back and forth between ROM and All-RAM mode is done on 
the CoCo 3, as far as I know.  I assume on startup that the entire 
ROM space from 32768 to the top of memory is copied into RAM.  You 
should be able to patch the disk ROM the same as you can for any of 
the other BASIC ROMs.

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