CreatiVEmu Forum

Here's some notes I put together on the BIOS functions used by most ROM cartridges.

If nothing else it saves me having to re-discover them when Tom has an idea

Great, thanks a lot

Again i am amazed! Great work!

The whole concept of disassembling and reverse-engineering the BIOS is like a book with seven seals inside a box with a key that is a riddle wrapped in an enigma to me :0)

Cheers, TOM:0)

Yes Tom, and i will need it for my crazy project i start. Is not about the i/o card

Oh! and Ah! the suspense! Looking forward! Cheers, TOM:0)

what are the differences between CV BIOS and Laser2001/Salora one ? Do they boot differently? e.g. does the Laser one jumps to BASIC instead of Cart ?

nippur72 wrote: ↑

Mon Mar 14, 2022 7:21 am

what are the differences between CV BIOS and Laser2001/Salora one ? Do they boot differently? e.g. does the Laser one jumps to BASIC instead of Cart ?

Salora Manager and Laser 2001 are the same - give or take the keyboard mappings.

At power on - a check is made for ROM at $B000 by copying one page (256 bytes) from ROM $FBD6.

If these compare - then it's assumed to be RAM, a further check for DISK ROM - then boot BASIC.

They do handle the demo modes differently for say a cassette game. As cassette games load to RAM - a reset would wipe them out.

The check for "have I seen this ROM before" is just compare the vectors at $200-$203 with $BFFC-$BFFF. When these are not the same, a ROM would start demo mode.

For tape loaded games - you just set them by copying before jumping to $FF76, which bypasses the initial RAM check above.

The only difference for games is that there is no demo mode when loaded from cassette.

The keyboard is also unavailable - as the matrix for the PIA is considerably different and they chose not to keep them compatible.

In short - if you have a game on ROM cartridge, which does not use keyboard, it will be the same as a CV.

If you load from tape - there's no demo mode.