Right, I guess I'm just regergitating but...
The 13th address line is simply the high enable /CE line on the ROM... so it
essentially does drop it... because everything is on the same bus
TIA/RAM/ROM the CPU has to have a way to tell each item on the bus which one
it is addressing at that time, so the 13th address line on the cart is the
only cartridge line that is not shared with anything else... which makes it
hold a special place in my heart :-). This allows sneaky circuitry in the
cartridge to read and process functions on the current address, even if the
cartridge isn't being addressed at all, which is what FE and 3F
bankswitching use....
--Chris
----- Original Message -----
From: "Eric Ball" <ericball@xxxxxxxxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Sunday, December 08, 2002 5:55 PM
Subject: Re: [stella] The mother of all bankswitching trickery :-)
> From: "Glenn Saunders" <cybpunks2@xxxxxxxxxxxxx>
> > The 6507 has 13 bits of available addressing off the chip through the
> > pins. The 2600 throws away a bit on the way to the cart port.
>
> Not quite. The cartridge connector has all 13 address lines (A0-A12), but
> typically A12 is used as a positive chip select or output enable. Thus FE
> bankswitching is possible, because the cartridge can monitor all memory
> accesses.
>
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