SD Interface for Plus 1

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Ramtop
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SD Interface for Plus 1

Post by Ramtop » Fri Oct 11, 2019 8:56 pm

Hi All,

The question that most comes up when people ask me about the ElkSD64 is "does it work with a plus 1?". To which the answer is, of course, no. But it got me thinking about doing something that would fit a Plus 1, especially when I obtained one thanks to the excellent Mr Dave Hitchins, of this parish.

After some false starts and much head scratching over Acorn's often less than precise documentation, I've now got something that works. It's basically a cut-down ElkSD64, with only 16K of flash and SW RAM as opposed to 32K of each on the ElkSD64. Just enough to run the sideways version of MMFS.
p1_3.jpg
p1_2.jpg
p1_1.jpg
Pictures are of the prototype, which is fully functional. Final boards will have gold plated contacts, the prototype is just HASL as I'm cheap and didn't want to spend any more than necessary on PCBs that may not have worked at all. :D

The hardware is mostly now fixed except for minor tweaks but there's still some room to add to the CPLD programming. I'm thinking of a register to switch out the default SW MMFS and boot with the standard version, which would free up the 16K of SW RAM for other use while retaining SD capability. I'm hoping to have a very limited number of finished boards available by the end of the month or early next month.
Gary

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daveejhitchins
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Re: SD Interface for Plus 1

Post by daveejhitchins » Sat Oct 12, 2019 9:43 am

Great work, Gary . . . =D>

Noticed you’ve placed the components on the side facing the keyboard (not that it, probably, matters with surface mount components?). This will give you the minimum space in the cartridge slot - especially with a case around it!

If it would help(?) I can send you templates for two sizes of PCB, the ‘standard’ Acorn Cartridge case and the 3D cartridge case design that I use. Let me know . . .

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

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CMcDougall
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Re: SD Interface for Plus 1

Post by CMcDougall » Sat Oct 12, 2019 9:49 am

:shock: =D> =D> =D>
ImageImageImage

Ramtop
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Re: SD Interface for Plus 1

Post by Ramtop » Sat Oct 12, 2019 11:11 am

daveejhitchins wrote:
Sat Oct 12, 2019 9:43 am
Noticed you’ve placed the components on the side facing the keyboard (not that it, probably, matters with surface mount components?). This will give you the minimum space in the cartridge slot - especially with a case around it!
For once I actually planned ahead here and measured to make sure it'll fit! :D

The final board won't have the pin headers, so the tallest component is the SRAM at 2mm tall. Combined with the case wall I only need 4.5mm clearance from the PCB, which the cartridge slot accommodates easily.
Gary

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0xC0DE
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Re: SD Interface for Plus 1

Post by 0xC0DE » Sat Oct 12, 2019 1:58 pm

shut_up_and_take_my_money-t2.jpg
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Elk2019
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Re: SD Interface for Plus 1

Post by Elk2019 » Sun Oct 13, 2019 3:24 pm

I am already the proud owner of your superb Electron MicroSD Interface Mk2.
Having recently acquired a Plus-1 expansion unit, I was delighted to learn that you have created an SD Interface for the Plus 1. I will definitely be getting one. Then I will finally be able to play some games using a joystick! What will base PAGE memory be set at and will the finished product have a case?

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Re: SD Interface for Plus 1

Post by Ramtop » Sun Oct 13, 2019 4:54 pm

For the Plus 1 board PAGE will be at &E00. The cartridge has 16K of sideways RAM on it so none of the Electron's memory is used up.

Current plan is there will be a case (same colour and general look as the ElkSD64) but I'm not sure if the first batch will have cases by default, it may be an optional extra. Making cases for the ElkSD64 is presently keeping my 3D printer very busy indeed, not sure how many Plus 1 cases I can squeeze in. If interest in the first batch is strong enough to justify it I may grit my teeth and invest in a second printer.

PCBs for the initial batch have been ordered. I'll post when I have something more to show :)
Gary

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Re: SD Interface for Plus 1

Post by mr-macrisc » Thu Oct 17, 2019 10:20 am

You can pop me down for one.

Is this a cartridge that will work in master and elk?

Regardless if it’s master/elk or elk only my name is a defo on list please

John

Ps wee though if it’s elk only why not a wee switch and couple extra tracks to make it work in both?

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Re: SD Interface for Plus 1

Post by Ramtop » Thu Oct 17, 2019 12:43 pm

It only works in the Elk, I'm afraid. Hardware wise, you're right, it's not a big deal to make the board Master compatible. But actually getting it to work would require more complexity in the CPLD programming and a master version of MMFS stored in the flash chip.

Now, this isn't insurmountable. I over-specced the CPLD (it has twice the logic of the one used in the ElkSD64 and more IOs) so I can add new stuff, and there are holes for a jumper on the PCB that could be used to switch the flash between Elk and Master versions of MMFS; the Master MMFS would need to be a Frankenstein hybrid of the normal Master MMFS and the Electron EPP hardware driver (as that's the interface the card implements for driving the SD card), no idea if that will work on not.

But none of that is a priority because...tada...there's probably going to be a specific Master SD cartridge. Because the Master has plenty of RAM on board a Master-only cartridge can do away with the SRAM chip and use a small CPLD with less IOs, so it will be cheaper to build. I've designed and ordered the PCBs for this, it's really a question of whether I can cobble together a build of MMFS that will work with it. My 6502 coding skills are not the best and I'm reluctant to do more than minimal modifications to the code.

PCBs for both the ElkSD-Plus1 and the Master board are in production and I hope to have them late next week. I've also printed the first case, it's ugly but it works and unlike the ElkSD64 it uses screws rather than glue. Also managed to get paging working on the prototype ElkSD-Plus1 board, so 64K of flash and 32K of RAM can be accessed by writing to a register; I'm thinking of putting multiple versions of MMFS in flash. I'd really like to have both standard MMFS and MMFS2 on board, selectable either by jumper or by a register write.
Gary

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marcusjambler
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Re: SD Interface for Plus 1

Post by marcusjambler » Thu Oct 17, 2019 2:20 pm

Please put me down for one built board :D

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Elminster
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Re: SD Interface for Plus 1

Post by Elminster » Thu Oct 17, 2019 3:00 pm

Ramtop wrote:
Thu Oct 17, 2019 12:43 pm

But none of that is a priority because...tada...there's probably going to be a specific Master SD cartridge.
Darn now I will have to update the hardware list again for Master version :twisted:

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Re: SD Interface for Plus 1

Post by Steve1234 » Thu Oct 17, 2019 3:54 pm

Put me down for 1 please

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0xC0DE
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Re: SD Interface for Plus 1

Post by 0xC0DE » Thu Oct 17, 2019 4:18 pm

I think it was pretty clear I'm interested in buying one, right? :mrgreen:

By the way, I'm also interested in the Master version. Is it at all possible to create one that keeps PAGE at &E00 and does not use any kind of RAM of the Master itself, i.e. to have SWRAM on the Master version as well? Some games and most notably demos need all the RAM they can get their hands on (looking at you Bitshifters)
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Ramtop
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Re: SD Interface for Plus 1

Post by Ramtop » Thu Oct 17, 2019 6:51 pm

Thanks for all the expressions of interest! They've given me enough confidence to up the first batch size; I was only going to do half a dozen Plus 1 boards, but that clearly isn't going to be enough.

The Master version is still very much up in the air right now. The simple no-RAM Master specific board ("MasterSD" as I'm imaginatively calling it) is really intended as something that can be sold cheaply on Ebay for people who've bought a Master and just want a memory card interface that doesn't require opening the computer up to fit a ROM and fiddling about underneath with cables. Barring a technical issue this one will almost certainly go ahead; the design has 100% component commonality with the ElkSD64, so I won't get stuck with a pile of useless components if it doesn't sell. The only risk is the PCBs, which are relatively cheap.

I may -- thinking out loud, here -- also do something for the Master with some RAM on it. Possibly a tweak of the ElkSD-Plus1 PCB (which isn't Master compatible in its current form). But that is still some way off, finishing the ElkSD-Plus1 has priority at the moment.
Gary

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0xC0DE
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Re: SD Interface for Plus 1

Post by 0xC0DE » Thu Oct 17, 2019 6:58 pm

No problem. We can wait an extra week :mrgreen:
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Re: SD Interface for Plus 1

Post by mr-macrisc » Fri Oct 18, 2019 11:05 am

Brilliant, will likely be having one of each then :)

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