[Coco] CoCo BASICS - clarification on the differences?

[Arthur Flexser]

There's actually a way to test for what Extended Basic will do when you
have only 4K of RAM available, if you have a CoCo 1 with a Color Basic
version that checks on startup whether the machine has 4K.  (This test was
eliminated in later Color Basic versions for CoCo models where only 16K and
64K were available.)

Anyway, if you hold down the shift and break keys and hit reset, it fools
the machine into thinking it has 4K.  You find that only very few commands
work;  most give an OM error with Extended Basic.  The few commands that
work are generally ones that have no arguments, like CLOADM.

(This is the Basis of the shift-break-reset method of breaking copy
protection that was written about in one of Marty Goodman's Rainbow
columns.  On one of these machines that checks for 4K, you can break out of
a copy-protected program with shift-break-reset and then use CLOADM and
EXEC to run a cassette program that will copy memory contents and return
you to 64K mode.)

Hmm, I wonder if shift-break-reset will work under an emulator?

Art



On Tue, Apr 4, 2017 at 9:28 PM, Mathieu Bouchard <matju at artengine.ca> wrote:

>
> Nope, ECB1 takes 16k of ROM, that is, 8k of ROM for CB itself which is the
> main programme, and then a 8k of ROM that is a plugin for CB that turns it
> into ECB1.
>
> Shadow RAM is when you use RAM to hold a copy of ROM, which makes them
> modifiable using POKE (same feature exists also on the PC, on which the RAM
> was also faster than ROM, but on the Coco you don't have that speedup). For
> Cocos that have less than 64k, this feature is disabled and irrelevant.
>
> The reason ECB1 would "require at least 16k" is because 4k is too tight
> when using graphic modes (PMODE). CB's own reserved RAM always takes the
> first k of RAM, then 32x16 text/semigraphic mode takes the next half k, and
> then you have 2.5k left for your tokenised BASIC program, plus all your
> strings (A$,...) and arrays, plus the graphics mode RAM (which can't
> overlap the text mode RAM). PMODE 0 takes 1.5k per screen ; the other
> PMODEs take either 3k or 6k per screen.
>
> Technically, there is enough room for using ECB1 or ECB2 with 4k as long
> as no graphics are used, or if only PMODE 0 is used and the BASIC programme
> is very tiny, but it doesn't mean that the authors bothered to make ECB
> able to run with 4k of RAM, I don't know.
>
>
> Le 2017-04-04 à 10:35:00, Steve Strowbridge a écrit :
>
> I think you got all the answers, but here's what I think I know/remember.
>> The first CoCo had two options, Color BASIC and Extended Color BASIC.
>> Color BASIC would run with as little as 4K, but Extended Color BASIC
>> required 16K of RAM because I think the ROM itself was 8K
>>
>
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> | Mathieu BOUCHARD --- tél: 514.623.3801, 514.383.3801 --- Montréal, QC
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