How many kb in a cartrige can an atari 2600 handle?

[meltdown71835]

I been researching the atari 2600 for programming purposes and I was wondering, how many kilobytes in a cartrige can an atari 2600 handle. I just starting researching this machine so I may not be correct in the wording. Any help would be appreciated.

[Paul Slocum]

It can address 2k. But some cartridges use bankswitching to get up to 8k, 16, or more.

 

-Paul

[meltdown71835]

What is bank switching?

[Nukey Shay]

Changing where you put your money. j/k

 

Bankswitching is a method of accessing more memory than the system is designed to access. Basically, it's like putting one playing card on top of another...both cards are still there, but you can only "see" one at a time.

[Skatepunk60]

nice explanation dude thanks

[+bcombee]

Actually, the 2600 can directly address 4K of ROM. Bankswitching is done byhaving special memory addresses decoded by the cart hardware and used to select another bank of memory. It might look like

 

0x0000-0x0FFF bank 0 (2K)

0x1000-0x1FF8 bank 1 (almost 2K)

0x1FF9 - when accessed, select A into bank 1

0x1FFA - when accessed, select B into bank 1

0x1FFB - when accessed, select C into bank 1

0x1FFC - when accessed, select D into bank 1

etc...

 

This gives a constant 2K of memory at the low end of the cart, and a switchable 2K at the top of the cart, depending on the last address in the small range that was accessed.

 

[ 05-31-2002: Message edited by: Ben Combee ]

[Nukey Shay]

You might add that you will be at the same point in memory in the new bank after it is swapped.

[Thomas Jentzsch]

Yup, the address space is 4K.

 

AFAIK the largest ROM inside a cart are 64K, but theoretical you could also do 1MB (256 banks) or even more.

[Pitfall Harry]

Is it theoretically possible to jamb a miniaturized Nintendo 64 system board and one N64 cartridge game into an empty Atari 2600 cartridge case? The N64-in-an-Atari cart would have the standard 2600 cartridge circuit card interface so that it could be slotted into a standard VCS, but it would only use 2 lines for power, one line for RF out, a few more lines for Joystick port inputs, and it would bypass the rest of the 2600 console circuitry.

 

It would be kinda cool to pop a 2600 cart into any old VCS and play something as visually dazzling as Legend of Zelda: Ocarina of Time.

 

Ben

[Nukey Shay]

I doubt it...all that conversion would take more power than the port handles.

[sdrake]

quote:

---

Originally posted by Pitfall Harry:

Legend of Zelda: Ocarina of Time

.

---

 

 

Arrgg, no Zelda on Atari!

[meltdown71835]

Whats an better example of bank switching? I don't get what your saying. Is it like switching to 2k then to another 2k?

[Paul Slocum]

Doing! I guess my brain is fried. The Atari can access not 2k but up to 4k. I suppose I should know that since I've been sitting here all day coding a 4k game!

 

The following document explains bankswitching:

 

Bankswitching Info

 

-Paul

[Nukey Shay]

I think that the best method of bankswitching (for beginners) would be the Robotank method...the other block is called up whenever you jump to a subroutine, and switched back automatically when the sub ends. That way, you never have to match up address locations when you switch.

[Paul Slocum]

That's a neat method. I never read about that one before. But I don't think there's currently a way to make cartridges that support anything except F4, F6 and F8 bankswitching. So using Activision's FE method would limit distribution to emulators and Cuttle Cart.

 

-Paul

[Nukey Shay]

True, but it makes coding much easier for a beginner. Once the source code is fully working and understood it could pave the way to using the more common techniques.