CreatiVEmu Forum

Thanks Tom. I didn't dare mentioning the Meg SD cart cause I wasn't too sure if it used a modified bios at $f800 (bypassing the existing bios entirely) or in the usual 32k rom space.
Also cv mark 1 and 2 have different address lines so it's important to know if and how you can use the upper 16k on both.

MADrigal wrote: ↑

Tue Mar 28, 2023 6:25 pm

Also cv mark 1 and 2 have different address lines so it's important to know if and how you can use the upper 16k on both.

The upper 16k can be used on mark 1 and mark 2 without problems... (CSL and MegaSDCart work in both revisions)

but i think there always needs to be the 2k BIOS (either the original or a modified one, but then again even that could be replaced by something totally different (if someone wants to create a new BIOS :0) ))

Cheers, TOM:0)

I believe as long as there's something the 6502 accesses and executes at startup, anything would do. Bios, or a game or a program doesn't matter. What is important is to know whether the console has logic suitable/sufficient to disable the original bios so it can be bypassed. thanks for confirming this!!

Here is a short "summup" of the cartridge-port address-signals, that can be used on both revisions...

The MK II port has replaced a few signals, that where present on MK I with signals needed to allow for an external CPU...

The MK II cartridgeport misses:
PIN 17: A15 (replaced by /CSW)
PIN 18: A14 (replaced by /CSR)
PIN 36: +12V (replaced by "switch to external CPU" signal)

Instead of the missing A14 and A15 the "16k block-select signals" can and should be used to address:
PIN 29: /ROM1 ($8000 - $BFFF)
PIN 32: /ROM2 ($4000 - $7FFF)
PIN 33: /ROM0 ($C000 - $FFFF incl. the 2k BIOS)

/ROM0 is on both revisions wired so, that it first goes to the cartridge port and "normally" an inserted cartridge would shorten the /ROM0 on PIN 33 to /ROMR on PIN 34 to "enable" the BIOS selection. That´s also why a Creativision without cartridge does "nothing" when powered on...

But /ROM0 could also be used to select an external BIOS/Program on the cartridge and not connect it back to /ROMR to use an external BIOS (like in the CSL Cart or MegaSDCart). Also only "parts" of the original /ROM0 select can be given back to /ROMR. That makes it possible for the parallel I/O Modul to use part of the /ROM0 addressroom and still use the original internal BIOS.

here is the pinout again to round this up :0)

Cheers, TOM:0)

Excellent Tom this clarifies everything
It would be good to wrap all the info in a single document or article to share from the website, to give it more visibility.

@username@ wrote: ↑

Tue Mar 28, 2023 11:30 am

I took the executive decision to fix the byte at $7223 for BASIC - saves writing and having a panic attack

Can you please share the patched BASIC rom here?

The ROM is not patched as such, only when it's injected into the image.

Attached is BASIC83B with the entire CVDEMO tape included, in both flat and AB images.

Use CLOAD or CRUN to load from the now free ROM space.

Enjoy!

@username@ wrote: ↑

Tue Mar 28, 2023 11:46 pm

Attached is BASIC83B with the entire CVDEMO tape included, in both flat and AB images.

Use CLOAD or CRUN to load from the now free ROM space.

Enjoy!

Hi @username@,

i gave the cartimage a go on real hardware and it works like a charme! :0)

PS: I tried the "flat" version.

Can you please provide a small "how to" get a BASIC Program in the right format / cartridgespace for this awesome design?

Cheers, TOM:0)

Scouter3d wrote: ↑

Wed Mar 29, 2023 6:06 am

Can you please provide a small "how to" get a BASIC Program in the right format / cartridgespace for this awesome design?

There is no actual design - more a kind of organic cobbling together

I've attached the DIY manual and tools - but I will probably update the utility part over time, as I'm sure there will be a wee buggette waiting for me!