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AuthorTopic: Launched a DIY A501 Replacement Project  (Read 1296 times)

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Offline kamiga

Launched a DIY A501 Replacement Project
« on: October 10, 2013, 03:04:38 PM »
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
 

Offline magnetic

Re: Launched a DIY A501 Replacement Project
« Reply #1 on: October 11, 2013, 12:06:51 AM »
cool project man, but why not just buy a used 501? not like they are rare lol
bPlan Pegasos2 G4@1ghz
Quad Boot:Reg. MorphOS | OS4.1 U4 |Ubuntu GNU-Linux | MacOS X

Amiga 2000 Rom Switcher w/ 3.1 + 1.3 | HardFrame SCSI | CBM Ram board| A Squared LIVE! 2000 | Vlab Motion | Firecracker 24 gfx

Commodore CDTV: 68010 | ECS | 9mb Ram | SCSI -TV | 3.9 Rom | Developer EPROMs
 

Offline Oldsmobile_Mike

Re: Launched a DIY A501 Replacement Project
« Reply #2 on: October 11, 2013, 05:07:31 AM »
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!
Amiga 500: 2MB Chip|16MB Fast|30MHz 68030+68882|3.9|Indivision ECS|GVP A500HD+|Mechware card reader + 8GB CF|Cocolino|SCSI DVD-RAM
Amiga 2000: 2MB Chip|136MB Fast|50MHz 68060|3.9|Indivision ECS + GVP Spectrum|Mechware card reader + 8GB CF|AD516|X-Surf 100|RapidRoad|Cocolino|SCSI CD-RW
 Amiga videos and other misc. stuff at https://www.youtube.com/CompTechMike/videos
 

Offline kamiga

Re: Launched a DIY A501 Replacement Project
« Reply #3 on: October 11, 2013, 01:55:09 PM »
Quote from: Oldsmobile_Mike;749792
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!


Yeah, in general I'm happy to see more new hardware in the amiga scene. Every extra breathe of life we can blow into the amigas is good.  This is a learning project for me,  but helps sustain the existing machines I have....

Yes,  extending this project to support 1mb should be easy enough.  Where do they get the extra address bit?

@magnetic: more about the journey than the destination my friend.

Thanks
Kamiga
 

Offline psxphill

Re: Launched a DIY A501 Replacement Project
« Reply #4 on: October 14, 2013, 02:15:39 AM »
Quote from: magnetic;749752
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.
« Last Edit: October 14, 2013, 02:20:28 AM by psxphill »
 

Offline kamiga

Re: Launched a DIY A501 Replacement Project
« Reply #5 on: October 14, 2013, 02:56:51 AM »
Quote from: psxphill;750083
This could actually be quite interesting for internal expansion. You could implement something like the kcs PowerPC, or ide or whatever.

Yup, and this thought definitely hasn't escaped me.

You could imagine that you could create any number of memory-mapped I/O devices.  Wikipedia says the Commodore 64 could bank switch between memory and the devices. [1]

I think useful throughput through the memory interface is somewhere around the color burst freq of 3.57mhz or so.  That's not horrible, and I have a couple decent ideas of how this could be used.

Thanks
kamiga

[1] http://en.wikipedia.org/wiki/Memory-mapped_I/O
« Last Edit: October 14, 2013, 02:57:31 AM by kamiga »
 

Offline TCMSLP

Re: Launched a DIY A501 Replacement Project
« Reply #6 on: October 14, 2013, 04:27:48 PM »
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 :D
A1200 50MHz 68030 16Mb, PCMCIA Ethernet, Indivision AGA MkIIcr
http://www.coherer.net Coherer: Electro!
 

Offline TjLaZer

Re: Launched a DIY A501 Replacement Project
« Reply #7 on: October 14, 2013, 04:45:31 PM »
I think that is a excellent project you got going there!  A new design, with modern components.  A learning project for you and a great product for us.  So what if there are a zillion battery damaged A501 cards out there, I say this is great.  Looking forward to the finished product and I would like to buy one from you.
Going Bananas over AMIGAs since 1987...

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Offline kamiga

Re: Launched a DIY A501 Replacement Project
« Reply #8 on: December 17, 2013, 02:41:10 AM »
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
 

Offline kamiga

Re: Launched a DIY A501 Replacement Project
« Reply #9 on: February 19, 2014, 11:05:43 PM »
Thought I'd mention that the finished PCB is fully working, although I'm continuing to do some testing on it.

I've added some photos:

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

Offline Lionheart

Re: Launched a DIY A501 Replacement Project
« Reply #10 on: February 20, 2014, 01:03:49 AM »
When will you have the schematics available?
 

Offline kamiga

Re: Launched a DIY A501 Replacement Project
« Reply #11 on: February 20, 2014, 05:11:41 AM »
Within a few days.  It's not very complicated.

The RTC portion is pretty textbook.  It worked the first time on the PCB with no prototyping done at all.  Just hooked it up, and it works! :)

The RAS/CAS/CE glue logic is only a few gates and a SR latch.

I'll try to put it up this weekend.
 

Offline kamiga

Re: Launched a DIY A501 Replacement Project
« Reply #12 on: February 22, 2014, 08:01:59 PM »
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