11 replies to this topic

[gusbucket13]

Please bear with me old hands, but in my ignorance I need to beg your help again.

Id like to know if such a thing as a DRAM daughter board could be made to expand the Jags own onboard meagre 2MB DRAM, if so would there be a limit to what the Jag architechture could usefully use, this I believe would allow much bigger CD ROM games to be written and run on the Jag.

I was prompted to propose the Idea when I saw the BJL modification process being done in a how to article on the web.

Cheers
Gusbucket13

[Thunderbird]

gusbucket13 said:

Please bear with me old hands, but in my ignorance I need to beg your help again.

Id like to know if such a thing as a DRAM daughter board could be made to expand the Jags own onboard meagre 2MB DRAM, if so would there be a limit to what the Jag architechture could usefully use, this I believe would allow much bigger CD ROM games to be written and run on the Jag.

I was prompted to propose the Idea when I saw the BJL modification process being done in a how to article on the web.

Cheers
Gusbucket13

I'm sure it's possible, but since the Jag uses so many surface mount DRAM chips it would be very delicate surgery to make it work. I suspect only a handful of people would attempt such a feat and with such a small percentage of owners of expanded Jags nobody would make games specifically for them.

[Clint Thompson]

I see where he would and why he would want to add more ram to the Jaguar... I'm unsure on how much you could actually add... but if you wanted to load a ROM from the Jaguar into the High temp memory and then have it emulate as a cart and load what info it needs into the 2mb.

That would be awesome! As if you could make an external device (DSP? I dunno) (cart?) that had 4-6MB of ram onboard, so when you loaded a CD with a ROM image(for example) it would load it into this RAM and act as a cart emulator... this way, no one would have to buy expensive carts again.
I would think onlyl minimal modifying would need to be done to the code, if any, maybe just a loader program. That and it would be much better then messing with a Flash Cart... (as they tend to DIE after years of use)

How expensive would the inital cart be? Maybe around the price of 2-3 new Jaguar games, but if someone were to release something like that with the features, you bet I'd put my $175 down!

Clint Thompson

[Punisher5.0]

I would say that it is possible to expand the Jaguar memory because the system was originally suppose to have 4mb. I would modify my Jaguar if I had the supplies and at least one game that supports the extra memory.

[jaysmith2000]

Clint Thompson said:

How expensive would the inital cart be? Maybe around the price of 2-3 new Jaguar games, but if someone were to release something like that with the features, you bet I'd put my $175 down!

Clint Thompson

I second that! Very cool it would be indeed!

Jason

[gusbucket13]

I heard somewhere recently that the Jag could handle 6Mb of RAM which it what prompted my initial question,

I have seen that a lot of the new DRAM advertised on E Bay are tiny wafer thin credit card sized items for Laptops and start at about 4Mb - if only they could be used Im sure there would be internal room for such thin devices if only the hardwiring hookup could be sorted out.

The External High Ram Uploader Cart has its merits too If any of the more technically minded would care to investigate this further please contact me privately.

Cheers
Gusbucket13

[Matthias]

Hi!

The Jaguar could handle up to 4MB internally. At the moment the
2MB it really has are mirrored, what might indicate that exchanging
the currently used DRAM-chips with pin-compatible ones of twice
the capacity could be possible.

But there is still the cartridge port, which has all the necessary
control-signals (/OE = Read, /WE =Write and so on), so putting
some SRAMS there (DRAMs still need a multiplexed addressbus
and CAS- and RAS-signals) and you have your additional RAM.
It might be slower, but who cares? Use it for seldom used
data.

Regards
Matthias

[ctsnlc]

Hi !

How does the Jag detect the width of the cartridge rom ?

The techref says it is automatic (pull-up/down resistors).
So, for a 8bits cart, you just don't have to connect D[8..31] ?

Cts.

[Matthias]

ctsnlc said:

How does the Jag detect the width of the cartridge rom ?

The techref says it is automatic (pull-up/down resistors).

So, for a 8bits cart, you just don't have to connect D[8..31] ?

I think this (the resistor) is only used for the startup of the system.
Later it decides it by reading four bytes from $802400.
If the system reads $04, it will use 32bit-access (The standard).
If the system reads $02 (i think), it will use 16bit-access.
Reading $00 will set it to 8bit-access (CD-ROM, FLASH,..)

And of course your software can change this when ever you want
(MEMCON1-register).

Regards
Matthias

[ctsnlc]

exact !
(from the boot rom):

LEA $F00000,A0 --> MEMCON1
MOVEQ #0,D0
MOVE.B $800400,D0 --> $800400 ,not $8002400
ANDI.W #$1E,D0 --> bits 1-4
ORI.W #$1861,D0
MOVE.L #$F032EC,8464(A0)
LEA $E00366,A1
LEA $400.S,A2
MOVE.W #$E,D1
L0015:MOVE.L (A1)+,(A2)+
DBF D1,-4(PC) L0015
JMP $400.S
MOVE.W D0,(A0) --> set MEMCON1


the problem is the "universal key" , designed for 32bits cartridge



am i right ?

Thanks !

[Matthias]

Hi!

ctsnlc said:

exact !  
(from the boot rom):  

 LEA       $F00000,A0 --> MEMCON1
  MOVEQ     #0,D0
 MOVE.B    $800400,D0 --> $800400 ,not $8002400

Sorry, i always tend to mix up these great numbers.

Quote

 ANDI.W    #$1E,D0 --> bits 1-4
 ORI.W     #$1861,D0
 MOVE.L    #$F032EC,8464(A0)
 LEA       $E00366,A1
 LEA       $400.S,A2
 MOVE.W    #$E,D1
L0015:MOVE.L    (A1)+,(A2)+
  DBF       D1,-4(PC)            L0015
 JMP       $400.S
 MOVE.W    D0,(A0) --> set MEMCON1


the problem is the "universal key" , designed for 32bits cartridge  
 
am i right ?

No: Although the UNIV.BIN-file covers the mentioned address space
(offsets $400-$403), its no problem to patch it. It's just UNIVERSAL!
I'm doing this all the day with my prototype card (I'm too lazy to
burn 4 chips, one is enough).

Bye
Matthias

[ctsnlc]

great !

Thanks for the infos !


regards,

Cts.