Another one of my hare-brained schemes has been ill-conceived and is on its way.

Felt like learning more about how the DRAM sub-system works on the Amiga, so I've set off to create a new redesigned A501 512K memory module for the Amiga 500's.

I'm documenting all of the DRAM timing of the RAS/CAS's/Write Enable/68K latches because I don't think it's been done before. And I don't see it in any of the official documentation.

So I'm starting to put up Logic Analyzer traces that have all the important details.

I'm using about USD $2.50 worth of glue logic parts, and < $5 memory SRAM chip.(SRAM?!@# the horror). The 56-pin header connector is one of the expensive parts, around $4.

The glue logic to convert DRAM RAS/CAS -> Chip Enable works in simulation, testing in hardware is forthcoming....

Project detailed at

http://www.techtravels.org/amiga/amigablog/?page_id=942

with blog posts at

http://www.techtravels.org/amiga/amigablog/?cat=28

Everything is open-source/open-hardware.

Constructive comments always appreciated.

Thanks
kamiga

Awesome!  I actually had a pretty tough time finding an A501-clone that didn't have battery damage, so hooray for new Amiga hardware!  Also you could probably make the 1MB ones that go to the A500+ with little modification to your design, those seem relatively rare (and expensive), also!

cool project man, but why not just buy a used 501? not like they are rare lol

This could actually be quite interesting for internal expansion. You could implement something like the kcs PowerPC, or ide or whatever.
 
The interesting thing about the KCS PowerPC is they made an A2000 adapter card
 
http://www.bigbookofamigahardware.com/bboah/product.aspx?id=336
 
which converts from zorro 2 into the RAS/CAS memory accessing of the a501.

I always wondered if a larger PIC would be capable of doing all the necessary magic to decode and store data;  I believe the larger PICs have 512Kb RAM.   I was considering something like this as a memory expansion on an 8 bit machine - I guess the difficult bit would be the timing, which may be even more of an issue on the Amiga.

Good luck on the 501 replacement though - stuff like this is a great learning exercise.  If others benefit from your work it's a bonus

I thought I'd mention that I just commissioned the creation of the PCB for this project.

http://www.techtravels.org/amiga/amigablog/?page_id=942

About (2) months (of nights and weekends here or there) from concept to PCB including building a mostly working solderless breadboard version.  Not too bad.  Not let's see if the darn thing works when it gets here.

Thanks

When will you have the schematics available?

As promised, schematics are now available.

I've got more stuff to put online, but just have to find the time.

I'd suggest downloading the PDF.  The plot-to-clipboard function of KiCad yields some fairly low-res images.

http://www.techtravels.org/amiga/amigablog/?page_id=942#Schematic