pcunningham.works
The Fourth ROM Level
The CoCo BASIC Keyword Reference now covers the CoCo 3. Super Extended Color BASIC 2.0 is the fourth ROM level, adding 28 entries: 182 in all, 176 with a worked example, 171 of them verified by running the code on real ROMs. Thirteen of the new entries carry a picture.
The first finding removed a worry rather than adding one. Despite the banner calling itself Extended Color BASIC 2.0, the CoCo 3 adds nothing at all to Color BASIC or Extended. All four name tables in the image are byte for byte identical to bas12.rom and extbas11.rom. The revision moved, the vocabulary did not, so there was no second Extended level to model.
Everything else had to be measured.
- Tokens were read off the machine, not assumed. Commands run $E2 to $F8, functions $FF $A9 to $FF $AD, and $FF $A8 belongs to nothing.
- The four HSCREEN modes gave up their bit depth to HCLS with a known color, since value 1 fills $11 at four bits per pixel, $55 at two and $FF at one.
- The palette is read out of the machine at every snapshot, because PALETTE can change any of the sixteen slots and a fixed table would quietly lie.
That last one paid for itself immediately. A CoCo 3 boots with green in slot 0, so HCLS 0 gives a green screen and not the black anyone would expect. A hardcoded palette would have been wrong on the very first example, and wrong in a way that still looks like a picture.
No screen capture is involved in any of this. The pixels come out of emulator memory, the same way the PMODE pages already worked.