Denial

Greets!

I am working on a project that fills an SRAM with a binary cartridge image and then boots the VIC.
So far my tests have worked, based on the information presented here...

http://comp.sys.cbm.narkive.com/0WNJAHD ... dge-format

What this indicates is...

Bytes 0,1 are the cold start program entry address.
Bytes 2,3 are the warm reset entry point address.
Bytes 4-8 are the sectret "a0CBM" auto start key (41 30 C3 C2 CD).

But I am starting to believe that this information is not correct.
In fact, every single 8K cart image I look at has an extra two bytes before the key.

Here is an example...



All of the images have 6 bytes before the secret key.
I have looked at many of the 8K ROMS from Zimmers, and they are all the same.

Can anyone shed light on this?
Either the info out there is wrong, or my HEX editor is playing tricks on me!

Thanks,
Brad

Your 'images' are PRG disk files. The first word of a PRG file is the load address. A true ROM image does not have this.

Thanks, problem solved!



I hunted around for different formats that ended with .a0 instead.
Now the secret key is at the correct offset.

I am not into emulators, so this is all new to me.
Wow, ".a0" files are not easy to find.

Brad

This is a property of disk drives, the computer has to know where to load a file. It's easy enough to 'convert' between PRGs and ROM images: just add/remove the first two bytes.

Wow, that's easy enough!
I though the entire source might have been redone to alter all of the jump addresses.

Thanks again,
Brad

BTW, there's nothing "secret" about the A0CBM signature, as it's usually called.