Re: [stella] The FAQ as it stands

Subject: Re: [stella] The FAQ as it stands
From: "Eric Ball" <eball@xxxxxxxxxx>
Date: Fri, 11 Oct 2002 08:51:58 -0400
On Fri, 11 Oct 2002, Manuel Polik wrote:

> > The 6507 has only 13 address lines, providing an 8K
> > address space.
> Is that true? Why do I need 8K BS then?

Chris Wilkson wrote:
> Yep, that's true!  But on the 2600, A12 is used for the cartridge
> enable line.  Thus, only A[11:0] are available as actual address lines.

> This is something that programmers sometimes forget or abstract away.
> But every day, us hardware guys lament the total lack of control lines
> in the cartridge port.  No read/write, no enable, not even a clock line
> for crying out loud!  All this to save 50 cents per VCS by going from 30
> to 24 pin connector.  ARRRGGGHHHH!!!!

In absolute memory map terms, $0000 - $0FFFF is taken by the TIA & RIOT.
Although neither uses the full address space, they don't decode all of the
address lines, causing the same registers & RAM to be shadowed at multiple
memory locations (like the RAM in the RIOT showing up at $0080 - $00FF and
$0180 - $01FF).

However, since the full address bus is available at the cartridge slot,
cartridges can snoop the bus and implement FE (aka JSR) and 3F
bankswitching where the trigger addresses were in the lower 4K address

Archives (includes files) at
Unsub & more at

Current Thread