[Coco] I think you'll like this (especially Allen)

[William Astle]

On 2025-03-20 20:02, Allen Huffman via Coco wrote:
> That said … does anyone know (Tim Lindner? William Astle?) if the ROM inside the CoCo 3 contains an UNMODIFIED Color BASIC and Extended BASIC, with the new code just overlaying on them once loaded into RAM?  Or is my above statement not true and they WERE allowed to modify the ROM?

There are a couple of modifications to the CB 1.2 and ECB 1.1 ROMs that 
are actually part of the ROMs. These look like binary overlay patches 
rather than reassembly so that tracks with them not having access to 
rebuild. The modified sections are in the system bootup code, which 
includes a bit that clobbers DLOAD. There's also a few bits related to 
text mode handling. Overall, it's minimal. The rest is handled by 
patching at bootup.

They could have done the bootup patches as binary overlays if they 
wanted to the same as the modifications actually in the ROM. However, 
because they needed to maintain compatibility with cartridges ROMs, most 
of these patches could not have been always active without possibly 
crashing the system on ROM calls (due to jumping into the E000+ area). 
By keeping the basically stock CB 1.2 and ECB 1.1 ROMs, maximum 
compatibility is retained. I have a strong suspicion that that is a 
major reason for the bootup patching having persisted instead of a 
burned in solution.

-- 
William Astle