On Wed, 21 Jun 2000, Glenn Saunders wrote:
> <EXTERNAL MEMORY>
> Atari 2600 ROM Memory Map
>
> E000-FFFF 8K Rom
> (shouldn't this be EFFF-FFFF? this is an 8K range above)
This should be $F000-FFFF.
> 1000-1FFF 4K Rom (mirror)
> 3000-3FFF 4K Rom (mirror)
> </EXTERNAL MEMORY>
Yes, this starts with $1000-1FFF and repeats every 8K. In other words,
if A12 is high, you're looking at the cartridge. A[15:13] doesn't do
anything, since they aren't bonded out of the 6507. They're present
inside the package, but they aren't connected to any pins, so they don't
do anything to the system.
> I am curious about something here. The 6507 has a 13-bit address
> bus. This comes out to 8192 bytes linear addressable. Don't these hex
> values jump around too much to fit within that address space?
A12 (the 13th bit) is tied to the ROM's enable pin, so you effectively
lose half of your address space. :(
-Chris
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