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Dragon memory map
Posted: Tue Jul 07, 2020 12:24 pm
by Yoruk
Hello there,
For learning purposes, I'm working on a custom 2*4k cartridge using standard 2732 eeproms.
I have issues finding the exact memory map for the cartridge. In a manual I found a cartridge between $C000 and $FEFF,
here it is $C000-$FF00 ("Cartridge ROM or DOS ROM") and also $8000 - $FF00 ("Basic and Cartridge ROMS")
Regarding the
CoCo memory map, it's $C000 - $DFFF ("8k Cartridge ROM").
So I'm a bit confused... Looks like the starting address is $C000. Adding 8k gives a stop address of $DFFF but I'm not sure. Regarding the
existing PCBs it looks like there is both 8k and 16k carts.
So is there a "standard" memory map for 8k games ?
Thanks !
Re: Dragon memory map
Posted: Tue Jul 07, 2020 2:50 pm
by sixxie
The 'R2' line on the cartridge port is active (low, IIRC) for all addresses $C000-$FEFF (map type 0). For 2 * 4K EPROMs I guess you'll also need to decode that with A12 for your chip selects (and A13 if you don't want your 8K of data $C000-$DEFF to be "shadowed" to $E000-$FEFF - 256 bytes missing there as they're SAM register access addresses).
Re: Dragon memory map
Posted: Wed Jul 08, 2020 6:44 am
by Yoruk
Thanks. $C000-$FEFF make sense, I'll retro-analyze a cartridge pcb to see if the IC are working in this area.
But maybe I'm missing something but I don't have any 'R2' signal on my cartridges pinout. Is the Dragon pinout similar to the
CoCo one ? I do have a /CTS ("Cartridge select signal") witch is used in my sample cartridge.
Re: Dragon memory map
Posted: Wed Jul 08, 2020 8:37 am
by sixxie
Oh, yes, pin 32 - CTS. Sorry, it's labelled 'R2' on the schematics.
..ciaran
Re: Dragon memory map
Posted: Wed Jul 08, 2020 9:08 am
by Yoruk
Thanks !
You confirm that the CoCo cartridge pinout is the same than the Dragon one ?
Re: Dragon memory map
Posted: Mon Jul 20, 2020 9:32 am
by tjewell
I can confirm 99.8% that they're the same (maybe there's a tiny difference I'm not aware of? I have some nagging memory that some Cocos have 12v and some don't on the cart port). But I know that a Coco cart game works when put in a Dragon, and the CocoSDC floppy emulator works in both.
Re: Dragon memory map
Posted: Mon Jul 20, 2020 11:57 pm
by Alastair
tjewell wrote: ↑Mon Jul 20, 2020 9:32 am
I have some nagging memory that some Cocos have 12v and some don't on the cart port.
I believe the CoCo 1 has 12V, but the later models do not.
Re: Dragon memory map
Posted: Fri Jul 24, 2020 7:41 am
by Yoruk
Thanks guys ! I'll study this.
Re: Dragon memory map
Posted: Mon Jul 27, 2020 7:15 am
by prime
CoCo 1 has 5V,12V *AND* -12V.
Dragon has 12V and 5V
CoCo 2,3 have only 5V.
What is important though is the line that carries -12V on the CoCo1, carries +12V on the Dragon. Though unless you are using them they can be left unconnected. Certainly for a ROM cart you shouldn't need them.
Cheers,
Phill.
Re: Dragon memory map
Posted: Wed Jul 29, 2020 5:59 pm
by Yoruk
That's make sense. And yes for a simple cart we don't need it.
Thanks !