Can an A590 be upgraded to 8Mb (+ more)

[sim085]

Hello,

The GVP HD8+ cn be upgraded to 8MB while the Commodore A590 can only be upgraded to 2MB.

My questions are; Can the A590 be upgraded (through some fix) up to 8MB? (Something like the fix to add 2MB Chipram to an A500 directly on the motherboard...)?

Also is 8MB the maximum ammount of FastRAM that can be added from the side expansion slot of an A500(+)? Or there is no limit (from the A500 perspective) but no company developed side expansions which could get more FastRAM?

Regards,
Sim085

[countzero]

sim085 wrote:
Hello,

The GVP HD8+ cn be upgraded to 8MB while the Commodore A590 can only be upgraded to 2MB.

My questions are; Can the A590 be upgraded (through some fix) up to 8MB? (Something like the fix to add 2MB Chipram to an A500 directly on the motherboard...)?

No.

Also is 8MB the maximum ammount of FastRAM that can be added from the side expansion slot of an A500(+)? Or there is no limit (from the A500 perspective) but no company developed side expansions which could get more FastRAM?

No.




OK, the 68000 has a bus address range of 16 MBs. Of this 8 MBs is reserved for chip ram and custom chips and IO in an Amiga. 8 MBs is reserved for Zorro 2 bus. The side expansion port is somekind of Zorro extension, so you can't have a memory upgrade bigger than 8 mb there. This holds for all 68000 based Amigas (2000, 600, no fast ram > 8 MBs)

AFAIK there's no logic in A590 to address more than 2 mb Fast RAM. Even if there were, you still would have to update the Autoboot ROM for extra RAM.

[Azryl]

Ok... I have heard but not personally confirmed this.. but the A590 can address 8megabytes of fastram with no modification IF you replace all the 256x4 ram chips with 1024x4 chips

Apparently this gives 4 times more memory with no modifications to the underlying ram logic.

The 1024x4 are extremely hard to get in the same DIP package as the 256's.

Hope someone else can add to this discussion

Az

[Zac67]

Hmm...

Never heard of this before but on checking the schematics there is a simple note "no connect on DRAMs are connected together to facilitate future conversion to 4M part (1Mx4)" - however, there's nothing more indicating that it's actually possible. It's not shown if the RAM controller U5 could provide muxed A9 for 1Mx4 operation, but it's fed the necessary inputs. You could check where pin 5 (NC) of the DRAMs leads to, but U5 is lacking the required output pin... Makes me seriously doubt whether this is possible.

As Azryl noted DIP20 packages of 1Mx4 DRAMs would be required, usually they come in DIP26.


Theoretically, the side expansion slot could be used for >8 MB RAM expansion, but only in conjunction with a 32 bit CPU upgrade to overcome the Zorro II space limitation. (Something in the line of a GVP A530, but with an extended RAM controller.)

[sim085]

Thank you very much for th answer. If I understand correctly an A590 can be upgraded to 8Mb if I find DIP20 packages of 1Mx4 but these seem not to exist.

[Zac67]

Makes me seriously doubt whether this is possible.

I'm not absolutely sure it's impossible, but unless you find someone who actually made it work I wouldn't believe in it.

PS: if you're really adventurous you could build an adapter board to fit DIP26 chips into the DIP20 sockets...

[whiteb]

Azryl wrote:
Ok... I have heard but not personally confirmed this.. but the A590 can address 8megabytes of fastram with no modification IF you replace all the 256x4 ram chips with 1024x4 chips

Apparently this gives 4 times more memory with no modifications to the underlying ram logic.

The 1024x4 are extremely hard to get in the same DIP package as the 256's.

Hope someone else can add to this discussion

Az

Nah, I do not think that is the case, if you could find 1024x4 that had the same pinout as 256x4, the Memory controller logic would still only map out 1mbit, or 256x4 of each chip any way.

256x4 basically means 4 arrays of 256kbit, 1024x4 means 4 arrays of 1024kbit.. but the memory controller would still only map out 256x4 on each chip (Given the physical wiring of the A590 to the Ram).

But i think the biggest hurdle will be that 1024x4 will have different pins than 256x4 (I could be wrong).

[Zac67]

Since DRAM uses a multiplexed address bus, the change from 256Kx4 to 1Mx4 requires an additional address bit (10 instead of 9) which the RAM controller (U205, 16L8 PAL) would have to generate (U8 & U9). From the schematics I have, there's little to indicate that this is actually the case. U205's output pins are completely used up and there's no spare anywhere to generate that bit. Unless a later rev (than the 7 I'm looking at) added this somehow there's no way this could work.

The A2091 controller is identical apart from the form factor and I haven't heard of anyone making it work with 8 MB RAM either, so finding DIP20 1Mx4 RAMs is probably the easier task...