8-Bit cartridge signals

[arudzki]

All,

 

I have a hardware question regarding the carts in the 8-bit computers. Several of the signals are pulled low, I assume, when a window of memory is accessed (I think one of the signals is A000 - BFFF).

 

My question is, are these signal activated even if the cart doesn't "announce" itself to the system?

 

I'm thinking of putting some memory mapped hardware in a cart and using the signals for control. I don't know if the signals are active (including the /CS signal too) if the carts don't announce themselves to the system.

 

Any help would be appreciated.

 

Thanks

 

Tony

[Rybags]

Err... I don't think so.

 

The MMU or whatever equivalent logic the machine happens to use depends on the S4 and S5 inputs to "know" whether a cartridge is inserted.

 

In such cases, access to RAM at the relevant area $8000-$9FFF and/or $A000-$BFFF is then inhibited and the RD4/RD5 Chip Selects are activated instead.

 

Of course the exception comes in the form of certain carts like the OSS and AtariMax ones that have the ability to disable/enable the cart via software on the fly.

 

But, I believe the /CCTL should always work ($D500-$D5FF access). That allows carts which only have hardware registers mapped to that page, e.g. homebrew Covox, second Pokey @ $D5xx, RT8 cart.

[+bob1200xl]

Actually, the other way around. RD4 and RD5 tell the MMU that it has to activate S4 or S5 chip selects.

 

Bob

 

 

Err... I don't think so.

 

The MMU or whatever equivalent logic the machine happens to use depends on the S4 and S5 inputs to "know" whether a cartridge is inserted.

 

In such cases, access to RAM at the relevant area $8000-$9FFF and/or $A000-$BFFF is then inhibited and the RD4/RD5 Chip Selects are activated instead.

 

Of course the exception comes in the form of certain carts like the OSS and AtariMax ones that have the ability to disable/enable the cart via software on the fly.

 

But, I believe the /CCTL should always work ($D500-$D5FF access). That allows carts which only have hardware registers mapped to that page, e.g. homebrew Covox, second Pokey @ $D5xx, RT8 cart.

[atariksi]

Actually, the other way around. RD4 and RD5 tell the MMU that it has to activate S4 or S5 chip selects.

 

Bob

 

 

Err... I don't think so.

 

The MMU or whatever equivalent logic the machine happens to use depends on the S4 and S5 inputs to "know" whether a cartridge is inserted.

 

In such cases, access to RAM at the relevant area $8000-$9FFF and/or $A000-$BFFF is then inhibited and the RD4/RD5 Chip Selects are activated instead.

 

Of course the exception comes in the form of certain carts like the OSS and AtariMax ones that have the ability to disable/enable the cart via software on the fly.

 

But, I believe the /CCTL should always work ($D500-$D5FF access). That allows carts which only have hardware registers mapped to that page, e.g. homebrew Covox, second Pokey @ $D5xx, RT8 cart.

 

Does anyone sell a cartridge interface to breadboard sort of device so one can experiment with the cartridge port?

 

I remember when I was in college we ordered an ISA-slot breadboard where you can play around with the bus signals of the PC and added some ADC to use in our project to avoid the terrible beep.

[arudzki]

That allows carts which only have hardware registers mapped to that page, e.g. homebrew Covox, second Pokey @ $D5xx, RT8 cart.

 

Is there a list somewhere of what devices are located where in the $D5xx range?

 

 

thanks

 

Tony

[Rybags]

http://www.atarimax.com/jindroush.atari.org/acarts.html

 

There's a reasonably complete list there.

 

I don't think it has second Pokey listed, AFAIK it's never gone beyond a homebrew DIY thing.

 

In theory you could easily map 16 extra Pokeys to the $D5xx page via cartridge, but of course you'd end up with something almost as big as the computer's motherboard.