Re: [stella] 2600 Memory Map & Question

Subject: Re: [stella] 2600 Memory Map & Question
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Wed, 21 Jun 2000 15:29:29 -0400 (EDT)
On Wed, 21 Jun 2000, Glenn Saunders wrote:

> 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)

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.  :(


Archives (includes files) at
Unsub & more at

Current Thread