A500 trapdoor memory: free design

[radfoo]

Just quickly took some pics, sorry not the greatest just done them with my mobile.

https://goo.gl/photos/CUXaNDbWPqyHipv46

You should be able to see the section of pins for 1-20 look a bit ugly, thats the bit I ended up re-doing. Have checked continuity on them and they seem okay.

thanks

Oli

[PeteAU]

Originally Posted by radfoo

Just quickly took some pics, sorry not the greatest just done them with my mobile.

https://goo.gl/photos/CUXaNDbWPqyHipv46

You should be able to see the section of pins for 1-20 look a bit ugly, thats the bit I ended up re-doing. Have checked continuity on them and they seem okay.

thanks

Oli

Oh a 500+, I just edited the post with the jumper settings. You do need to open/cut the ENABLE jumper. I'm not sure if one chip will work using RAS1, but try it. It might need both chips, or one on RAS0, depending on what order kickstart checks them in.

[radfoo]

Originally Posted by PeteAU

Oh a 500+, I just edited the post with the jumper settings. You do need to open/cut the ENABLE jumper. I'm not sure if one chip will work using RAS1, but try it. It might need both chips, or one on RAS0, depending on what order kickstart checks them in.

Ah cool, thanks for the advice. Thought it might be best to get one chip working first so have dug out a normal A500 I have, though that still does not see the expansion. Sorry if I have missed something in the thread but do I need to set any jumpers on the PCB for 512kb expansion in a normal A500 (not plus)?

Thanks

Oli

[PeteAU]

Originally Posted by radfoo

Ah cool, thanks for the advice. Thought it might be best to get one chip working first so have dug out a normal A500 I have, though that still does not see the expansion. Sorry if I have missed something in the thread but do I need to set any jumpers on the PCB for 512kb expansion in a normal A500 (not plus)?

Thanks

Oli

Yeah it should just work on a normal A500 with default jumpers. Are you sure there's no solder bridges near the DRAM's pin 38-40? It just appears the traces lost a bit of their green solder-mask. Maybe buzz the traces with a multimeter continuity test. Pin 20 on the header also, I see a solder blob there.

It's not easy to debug, either it'll totally work, or completely not work

[radfoo]

Thanks for the advice. Will double check everything.

[appiah4]

Actually received the board today. Will be working on it in the coming weeks.

[demolition]

Just received the board this weekend and have just soldered it up and done a quick test.
I can report that it works perfectly in my A500+. Had to change some jumpers to make it work though, but luckily I had soldered headers on all jumpers (and cut the pre-existing connections) so I could easily change the settings.

Since I had desoldered 4 RAM chips, I decided to just fill out the board with 3 - who knows if I might get a Gary adapter for it one day so I could use it for 1.5MB in an A500. I will probably also put an RTC on it as it feels uncompleted without it, although my A500+ has one already.

The attached pictures show a successful memory test of all 2MB chip and a picture of the board which should be clear on how the jumpers should be set.

If I remove the jumper for the middle RAM chip, it runs with 1.5MB chip, however with the left jumper in the original position, no extra memory was detected.

Thanks again for providing such a lovely design.

Edit: It doesn't seem to make a difference whether the EN jumper is set or not.

Originally Posted by PeteAU

So it turns out 1.2 kickstart cannot support 1.5MB slow ram and just yellow-screens. But no problem with 1.3 or 3.1, I wonder why. Now I just need a 1MB Agnus to finish it off.

If you check out this manual for the ALFADATA RA5-2MB expansion, they also write that a 1.5MB config is impossible under KS1.2 but requires 1.3, although they do not specify why that is:
http://www.retro-commodore.eu/2017/0...-users-manual/

[PeteAU]

Originally Posted by demolition

Edit: It doesn't seem to make a difference whether the EN jumper is set or not.

I would think it's already cut on your motherboard then, because for a 500+ it needs to be off.

Originally Posted by demolition

Just received the board this weekend and have just soldered it up and done a quick test.
I can report that it works perfectly in my A500+. Had to change some jumpers to make it work though, but luckily I had soldered headers on all jumpers (and cut the pre-existing connections) so I could easily change the settings.

Since I had desoldered 4 RAM chips, I decided to just fill out the board with 3 - who knows if I might get a Gary adapter for it one day so I could use it for 1.5MB in an A500. I will probably also put an RTC on it as it feels uncompleted without it, although my A500+ has one already.

The attached pictures show a successful memory test of all 2MB chip and a picture of the board which should be clear on how the jumpers should be set.

If I remove the jumper for the middle RAM chip, it runs with 1.5MB chip, however with the left jumper in the original position, no extra memory was detected.

Thanks again for providing such a lovely design.

Cool. So only one succesfully made board? I think I sent out 8 of them.

I got a few PMs about them, but I've got none left. Maybe more in a week or 2 when I retry this gary adapter in a rev B...

[appiah4]

Originally Posted by PeteAU

Cool. So only one succesfully made board? I think I sent out 8 of them.

I got a few PMs about them, but I've got none left. Maybe more in a week or 2 when I retry this gary adapter in a rev B...

Still waiting for the SIMM modules to arrive unfortunately

[esel]

Originally Posted by PeteAU

This prototype is no good for 1MB chip RAM, but I see what I did wrong and could make it work for 1MB chip in the future.

Cheers,

Something new on that ?

[PeteAU]

Originally Posted by PeteAU

Re:Gary Adapter: This prototype is no good for 1MB chip RAM, but I see what I did wrong and could make it work for 1MB chip in the future.

Originally Posted by esel

Something new on that ?

Yes, the wheels are in motion on that. Waiting for slow PCB manufacture and Chinese new year delays...

[appiah4]

Right, so the SIMM arrived today. Cross your fingers, this should be done this weekend.

[PeteAU]

Hi,
Made some progress and got the gary adapter working with 1MB chip RAM. I also added pads for a 4th RAM chip on the bottom side, which gives my A500 a total of 2.5 MB. Then you can add 8MB fast RAM to max it out

This is basically a re-creation of a 80's AMRAM1M5, but with the benefit of allowing 1MB chip. It's got jumper switches which allow you to select between 0.5/1.0/1.5 expansion RAM.

I know the title of this thread says "free boards", but I can't do that anymore. I might have to charge a staggering €10 or so, any interest in that (DIY board)?

[dalek]

Hey Pete - looks good! Put me down for 2 please

[demolition]

Looks good indeed. I think €10 is a bargain, so I'd like one of these as well.

[Jope]

Brilliant! I edited the thread title for you, so you don't have to fence off questions. :-)

[esel]

great ! will you release the design ?

[fryguy]

Haven't read the whole thread, but will this board give my A500+ 1MB extra chipmem?
Is the RAM chips easily available somewhere?

[demolition]

Originally Posted by fryguy

Haven't read the whole thread, but will this board give my A500+ 1MB extra chipmem?
Is the RAM chips easily available somewhere?

Yes and yes. Just read post #1.

[PeteAU]

Originally Posted by Jope

Brilliant! I edited the thread title for you, so you don't have to fence off questions. :-)

Perfect thanks. I hope I'm not breaking some forum rule by selling a few boards (?)

Originally Posted by esel

great ! will you release the design ?

I just need to recoup some costs, cos I made a few duds before it actually worked And this'll fund my next thing, whatever that is (ideas?). Then I'll release the Rev B Eagle files in a few months.

So, if you want a rev B board (includes gary adapter, which you can cut out):

AUD$15 per board (this is around €10,70 euro) by Paypal 'friends & family' payment. Postage is at your risk, unless you want to pay for tracking.

Australia Postage:
AUD$1.00 for small letter - 1 board only (one stamp).
AUD$2.40 for "large letter post" (two stamps) + small cardboard 20mm box.
Add 50c for a priority label.
AUD$7.60 for a parcel - probably over-kill, but it's your option.

International Postage:
AUD$2.95 for letter post (in an envelope, taped to a postcard).
AUD$8.00 for large letter (in a bubble bag).
If you prefer a parcel, let me know, but it's a lot more expensive.

PM with your country and I'll give you details. If you send me an extra $1 I'll include the capacitors (tell me how many you want).

In summary, what you can do with this board is:
- 512K for A500, this can be CHIP or SLOW depending on Agnus. See post #1.
- Real time clock with coin cell battery, see post #14.
- 2MB for A500 with gary adapter, adds 0.5chip + 1.5slow. See post #53.
- 1MB additional chip RAM for A500+, see post #47.