A3000-to-A5000 ROM adapter

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myelin
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A3000-to-A5000 ROM adapter

Post by myelin » Mon Jan 07, 2019 6:35 am

Moving this from the in-system programmable ROM ("arcflash") project thread...

URL for this project: http://myelin.nz/acorn/a5k3krom

Here's a board that can be used as A5000-to-A3000 ROM adapter or an A3000-to-A5000 ROM adapter. I'm making it so people can use my "arcflash" boards (designed for A3000/A3xx/A4xx/A5xx systems) on A5000s too, but Joka80 is interested in the opposite (adapting an A5000 memory expansion board to work on an A3000), and I don't see why that wouldn't work too.

Here's the bottom (the A5000 side), with no space between the ROMs:
Screenshot 2019-01-06 18.30.01.png
The extra space on the board should overhang an empty part of the A5000 motherboard near the edge.

And here's the top (the A3000 side), with a 0.1" gap between each pair of chips:
Screenshot 2019-01-06 18.29.53.png
The extra space on the board here should overhang to the north; there's a tantalum capacitor (C22) up there, but I think there should be 0.2" of room to move before hitting it.

For the "normal" case (running an arcflash board in an A5000), I would solder four 32-pin chip headers on the A5KROM* spaces on the bottom and four 32-pin sockets on the A3KROM* spaces on top. For Joka80's case, I would do the same, except solder to the "wrong" footprints. (i.e. the headers on the bottom go underneath the A3KROM* footprints, and the sockets go on top, in the A5KROM* footprints.)
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Re: A3000-to-A5000 ROM adapter

Post by myelin » Mon Jan 07, 2019 8:30 pm

Here it is: https://github.com/google/myelin-acorn- ... dapter_pcb

All wired up; I need to verify it a bit more but I think this should work. I added a pin for A21 to easily connect it up to the flash board.
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Re: A3000-to-A5000 ROM adapter

Post by RobC » Wed Jan 09, 2019 4:27 pm

This is great =D> =D> :D

I have several spare A5000 8MB upgrades and I'd love to fit one to my A3000.

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Re: A3000-to-A5000 ROM adapter

Post by JonC » Wed Jan 09, 2019 5:19 pm

RobC wrote:
Wed Jan 09, 2019 4:27 pm
This is great =D> =D> :D

I have several spare A5000 8MB upgrades and I'd love to fit one to my A3000.
Umm, wouldn't that require an extra MEMC1a? or did I miss something.
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Re: A3000-to-A5000 ROM adapter

Post by steve3000 » Wed Jan 09, 2019 5:54 pm

Great work!

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Re: A3000-to-A5000 ROM adapter

Post by myelin » Wed Jan 09, 2019 5:55 pm

JonC wrote:
Wed Jan 09, 2019 5:19 pm
Umm, wouldn't that require an extra MEMC1a? or did I miss something.
Yeah, it’s not an easy upgrade! You’ll need to desolder your MEMC1A and solder on a socket, and you’ll need a complete 8MB A5000 upgrade with its second MEMC1A chip on board. Might need a longer ribbon cable too as it looked a little short in the pics Joka80 posted in the other thread.

Anyone who wants one of these boards, please PM or post here, because I’m about to do a parts order for the other project and I can get the bits for this at the same time! Looks like it’ll cost about US$20+shipping, so US$34 if you’re in the UK and a bit less if you’re in the USA. (The pin headers to attach to the ROM sockets are quite pricey.)
Last edited by myelin on Wed Jan 09, 2019 5:56 pm, edited 1 time in total.
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Re: A3000-to-A5000 ROM adapter

Post by RobC » Wed Jan 09, 2019 6:39 pm

JonC wrote:
Wed Jan 09, 2019 5:19 pm
Umm, wouldn't that require an extra MEMC1a? or did I miss something.
Yes - but the A5000 8MB upgrades I mentioned have dual MEMC boards :)

Still need to desolder the original MEMC1A from the A3000 PCB and fit a socket but I managed to remove the ARM2 and add an ARM3 upgrade.

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Re: A3000-to-A5000 ROM adapter

Post by steve3000 » Wed Jan 09, 2019 8:44 pm

RobC wrote:
Wed Jan 09, 2019 6:39 pm
Still need to desolder the original MEMC1A from the A3000 PCB and fit a socket but I managed to remove the ARM2 and add an ARM3 upgrade.
Also need to consider the clearance - you'll need to fit the A5000 expansion under the A3000 keyboard, and it'll have to avoid other components. Might just be possible, but looks tight. Alternatively could save a couple of mm by removing the A3000 ROM sockets and soldering the conversion board directly to A3000 motherboard... but that's a lot more work.

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Re: A3000-to-A5000 ROM adapter

Post by RobC » Thu Jan 10, 2019 9:08 pm

steve3000 wrote:
Wed Jan 09, 2019 8:44 pm
Also need to consider the clearance - you'll need to fit the A5000 expansion under the A3000 keyboard, and it'll have to avoid other components. Might just be possible, but looks tight. Alternatively could save a couple of mm by removing the A3000 ROM sockets and soldering the conversion board directly to A3000 motherboard... but that's a lot more work.
Ah - hadn't thought of that Steve - thanks for pointing it out.

Removing the ROM sockets is probably the way to go. It isn't too much of a hassle as I've replaced a few with battery damage in the past. Probably need an ultra-thin version of the conversion board too.

On a side note, did anyone ever produce an 8MB upgrade for the A3000? I can remember ARM3 upgrades being advertised but can't definitely recall anyone offering an 8MB upgrade.

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Re: A3000-to-A5000 ROM adapter

Post by steve3000 » Thu Jan 10, 2019 11:24 pm

Well, looking at an A3000 last night, there is actually more height clearance under the keyboard than I thought there was.

So I think you could get enough height, either but directly mounting the converter pcb to the motherboard or the 4-8mb ROM card to the converter.

However I'm now thinking it's the surrounding components and connectors on the motherboard which look more problematic to deal with - such as the keyboard connectors and battery to the left of the ROMS and possibly the 4mb RAM expansion to the right. Battery can be dealt with, but keyboard connectors are more problematic to move... (although I do have a set of spare connectors, so not impossible to relocate these if really necessary!).

There certainly was an 8mb expansion for the A3000, at least one. Unfortunately I can't find the link to the photo now, but it had a twin MEMC board with IDC cable to a custom RAM board sitting in the usual RAM upgrade slot. There was no sign of a ROM carrier board, so presumably you could get all the signals needed for the twin MEMCs from a wired connection between these two parts (unless there was additional wiring to the other side of the PCB...) Will see if I can find that photo.

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Re: A3000-to-A5000 ROM adapter

Post by myelin » Thu Jan 10, 2019 11:56 pm

steve3000 wrote:
Thu Jan 10, 2019 11:24 pm
There certainly was an 8mb expansion for the A3000, at least one. Unfortunately I can't find the link to the photo now, but it had a twin MEMC board with IDC cable to a custom RAM board sitting in the usual RAM upgrade slot. There was no sign of a ROM carrier board, so presumably you could get all the signals needed for the twin MEMCs from a wired connection between these two parts (unless there was additional wiring to the other side of the PCB...) Will see if I can find that photo.
That makes sense... along with the MEMC signals (Ras*, Cas*, Ra*), the RAM upgrade slot connects to the RAM data bus (Rd), which is connected to the ARM data bus (D) via a bunch of series resistors. I believe both upgrades just need the data bus, as they can get the ARM address bus from the MEMC socket.
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Re: A3000-to-A5000 ROM adapter

Post by RobC » Fri Jan 11, 2019 10:59 am

steve3000 wrote:
Thu Jan 10, 2019 11:24 pm
Well, looking at an A3000 last night, there is actually more height clearance under the keyboard than I thought there was.
Thanks for looking.
steve3000 wrote:
Thu Jan 10, 2019 11:24 pm
There certainly was an 8mb expansion for the A3000, at least one.
I thought I'd seen one advertised but wasn't sure. Might dig out some old AUs to see if I can find it.

I'll get my A3000 out as some point over the weekend and will see how much space the A5000 8MB boards need. Hopefully, at least one of them will fit!
steve3000 wrote:
Thu Jan 10, 2019 11:24 pm
Unfortunately I can't find the link to the photo now, but it had a twin MEMC board with IDC cable to a custom RAM board sitting in the usual RAM upgrade slot. There was no sign of a ROM carrier board...
myelin wrote:
Thu Jan 10, 2019 11:56 pm
I believe both upgrades just need the data bus, as they can get the ARM address bus from the MEMC socket.
Yes - the MEMC only deals with addresses so these RAM upgrades also need a databus connection. Guess it makes sense to take that off the ROM sockets in an A5000 and off the memory expansion in an A3000.

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Re: A3000-to-A5000 ROM adapter

Post by steve3000 » Fri Jan 11, 2019 12:48 pm

Makes sense...so there should only be a handful of signals needed between the 8mb RAM and twin MEMC board?

In which case, if you could replace the 4mb RAM in the A3000's 4mb upgrade with 8mb, then wire across the necessary signals (including the extra address line) to a twin MEMC board, you could avoid having the ROM board altogether?

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Re: A3000-to-A5000 ROM adapter

Post by RobC » Fri Jan 11, 2019 4:08 pm

steve3000 wrote:
Fri Jan 11, 2019 12:48 pm
In which case, if you could replace the 4mb RAM in the A3000's 4mb upgrade with 8mb, then wire across the necessary signals (including the extra address line) to a twin MEMC board, you could avoid having the ROM board altogether?
That's worth thinking about. I believe that the 4MB upgrade in my A3000 might well be the SIMM type so I could possibly put in an 8MB SIMM and just wire across the extra address line :idea: =D>

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Re: A3000-to-A5000 ROM adapter

Post by steve3000 » Fri Jan 11, 2019 4:17 pm

RobC wrote:
Fri Jan 11, 2019 4:08 pm
I believe that the 4MB upgrade in my A3000 might well be the SIMM type so I could possibly put in an 8MB SIMM and just wire across the extra address line :idea: =D>
I'm thinking of trying exactly the same, once can work out the required signals needed to patch across. Will keep you posted.

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Re: A3000-to-A5000 ROM adapter

Post by IanS » Fri Jan 11, 2019 4:37 pm

steve3000 wrote:
Fri Jan 11, 2019 4:17 pm
RobC wrote:
Fri Jan 11, 2019 4:08 pm
I believe that the 4MB upgrade in my A3000 might well be the SIMM type so I could possibly put in an 8MB SIMM and just wire across the extra address line :idea: =D>
I'm thinking of trying exactly the same, once can work out the required signals needed to patch across. Will keep you posted.
Would that work, I always assumed the RAM side of each MEMC would need to be talking to an independent set of RAM, the CPU side of the MEMC is largely paralleled up. Seem odd if you can link the "Ra<x>" signals from multiple MEMC's

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Re: A3000-to-A5000 ROM adapter

Post by RobC » Fri Jan 11, 2019 10:06 pm

I think the two halves of an 8MB SIMM have separate RAS signals and I think the address lines from the CPU effectively act as enable lines to the MEMCs but I'm not sure how the DRAM refresh works.

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Re: A3000-to-A5000 ROM adapter

Post by steve3000 » Fri Jan 11, 2019 11:01 pm

RobC wrote:
Fri Jan 11, 2019 10:06 pm
I think the two halves of an 8MB SIMM have separate RAS signals
Yes, that's what I understood was the case for 8mb SIMMs as they are dual-ranked...but I will be reading up a bit more thoroughly on the subject before making any plans :)

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Re: A3000-to-A5000 ROM adapter

Post by myelin » Sat Jan 12, 2019 8:36 pm

I'm pretty sure the two MEMCS will both expect to be driving the RA* lines all the time, and they'll most likely be on different refresh schedules too, so I doubt you'll be able to put them in parallel on a single 8MB SIMM.

The holy grail here (a project I'd love to take on sometime) would be a new FPGA-based MEMC, with a 512 entry CAM table and the ability to connect to 16MB of RAM. The most annoying part of this is that 68-pin PLCC plugs are expensive and hard to find, so it would be a very pricey upgrade.
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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Sat Jan 26, 2019 12:08 am

Hi myelin

Lovely to see the progress and indeed everybody discussing the A3000 8Mb upgrade. It’s definitley one of the ‘ultimate must have’ upgrades for any A3000 owner! :D

I’ll definitely be taking one of your converter boards once completed :D

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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Sat Jan 26, 2019 12:13 am

Here is the photo of an 8Mb A3000. It’s not clear but does give an indication somewhat of how it’s been set-up...
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Re: A3000-to-A5000 ROM adapter

Post by myelin » Sat Jan 26, 2019 1:11 am

Nice! I haven’t ordered any boards yet (parenting a 7 week old baby is consuming most of my spare time!) but hope to do so in the next month.

That A3000 RAM board looks very interesting! As I write the software for the Arcflash OS selector/bootloader, I’m getting more of the hang of how the MEMC works (with all its DMA channels and so on), and doing an FPGA replacement for a 16MB board is looking more and more feasible... waaaaay down the line though :)
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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Sat Jan 26, 2019 8:50 am

That’s so nice - congratulations about the baby! We are expecting our first baby girl in mid April :D

Yes, that A3000 memory board does look interesting, hence the idea of either using the Atomwide 8Mb upgrade kit with your converter board :D or using an 8Mb FPM module in an IFEL MA4K 72 pin memory expansion upgrade...there’s doesn’t appear to be any other wiring or modifications from what I can see to the A3000 motherboard...twin MEMC1A board (presumably with the PALS/GALS on it, directly connected to an 8Mb memory module, presumably FPM memory...

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Re: A3000-to-A5000 ROM adapter

Post by paulv » Sat Jan 26, 2019 10:35 am

myelin wrote:
Sat Jan 26, 2019 1:11 am
doing an FPGA replacement for a 16MB board is looking more and more feasible... waaaaay down the line though :)
If/when you do do this, it'd be useful to be able to configure the number of MEMC's in use for 4, 8, 12 and 16MB of RAM. This would assist in compatibility issues such as the one with ADFFS which can only operate on the older Arc's with up to 12MB of RAM because of the software trickery it uses to get things working on those machines.

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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Thu Jan 31, 2019 12:26 am

Hi myelin

Hope your well :D

I have managed to get a Simtec 8Mb upgrade kit (thanks to RobC) which is more compact and better suited to the A3000, but as the upgrade was originally designed for the A5000, we still need your adapter board :D

Do you have a rough idea on when the board will be ready? :wink:

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Re: A3000-to-A5000 ROM adapter

Post by myelin » Thu Jan 31, 2019 5:38 pm

Hah... it was waiting on me finishing two more designs (for the A3000 logic analyzer project) but now that I have a RISC PC, I think I’ll build an adapter board for it and then send the two adapters off for fabrication. So about three weeks?
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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Thu Jan 31, 2019 6:06 pm

That's great myelin - of course, no problem. Really looking forward to it :D

I will also pay for express shipping to the UK :D

This is one of the ultimate upgrades for the A3000 - 8Mb...

Below is the upgrade that I have received. Much more compacter than the Atomwide version as you can see, and Simtec used Hitachi HM514400CS6 60ns FPM memory chips on the one that I have. I do have the socketed twin MEMC board as opposed to the soldered twin MEMC board but this bears no difference I believe...same product code and writing on either...if anything the socketed version is handier incase you get a MEMC go down, easier to replace...
modules-med.jpg

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Re: A3000-to-A5000 ROM adapter

Post by myelin » Sun Feb 10, 2019 1:24 pm

Boards are being made as we speak... Joka80, I'll ping you with pricing details once some arrive and I can build you one :)
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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Sun Feb 10, 2019 4:48 pm

Awesome myelin! :D :D

Thank you very much...

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Re: A3000-to-A5000 ROM adapter

Post by Joka80 » Wed Mar 06, 2019 8:38 pm

myelin wrote:
Sun Feb 10, 2019 1:24 pm
Boards are being made as we speak... Joka80, I'll ping you with pricing details once some arrive and I can build you one :)
Hi myelin

Do we have any news or are we getting closer to the board being made? Exciting times ahead... :D

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