New DIY Project released: The MegaROM

[Bryce]

No need, I did some serious investigation into low voltage flash ICs last night, and I think I can make a very low cost write-able flash version. It will take a few weeks though, before I can confirm this and TFM has said he'll write the software needed to flash it.

Btw, in case anyone is thinking of making the MegaROM for themselves, you might like to wait a few days, I will release a Rev. B. version next week, which will allow you to choose whether the 8 ROMs (when using a 1Mbit EPROM) are 0-7 or 8-15 (for about same price, no extra parts except for a jumper). Of course if you don't need/want this option, then there's no point in waiting

Bryce.

[arnoldemu]

No need, I did some serious investigation into low voltage flash ICs last night, and I think I can make a very low cost write-able flash version. It will take a few weeks though, before I can confirm this and TFM has said he'll write the software needed to flash it.

Btw, in case anyone is thinking of making the MegaROM for themselves, you might like to wait a few days, I will release a Rev. B. version next week, which will allow you to choose whether the 8 ROMs (when using a 1Mbit EPROM) are 0-7 or 8-15 (for about same price, no extra parts except for a jumper). Of course if you don't need/want this option, then there's no point in waiting

Bryce.

excellent. I would love to buy a flash version and program it myself. Would it be possible to alter the pcb so that it could potentially be used to map into cpc+ cart space? so that it could become an alternative to programming carts. of course the basic cart would need to be plugged in, but would help me to make cart based games.

I don't know if it does this already...

it would need to look at bit 7 of the rom selection.

[Bryce]

The simple answer is, I haven't a clue. I've never looked at the CPC+ or the cartridges it uses, because I don't own a plus machine. Are they directly mapped into address space, or do they also share space like a standard ROMBoard? If so, which ROM numbers does a cartridge occupy? Can you point me to some information about this and I will investigate the possibilities.

The plan at the moment, is that it will work as a standard ROMBoard for ROMs 0-15, but it will use a special type of low-voltage flash chip, so that using the program that TFM writes, you can copy ROM images to it using the CPC (so no PC or EPROM programmer needed). Because it will use flash, it won't need a battery, and will (effectively) never loose the stored programs. And as always, I'll try to keep the cost to an absolute minimum.

I'll give you an update, when I've built the first prototype.

Bryce.

[eliot]

Just technical:
- is there a way to desactivate all the Roms with a Jumper for programs that don't support a lot of installed roms ?
- more advanced feature : possible to enable/disable ROM 0 and 7 ?  Hack-It rom in 0, Parados in 7.

- if not, what are the jumpers present on the boards ?

[Bryce]

Hi Eliot,
        it's all on the Wiki page, but here it is again:

Jumper 1 switches the MegaROM ROM 7 on/off, but it won't let you overlay the internal ROM 7 on a standard 6128. (See note below).
Jumper 2 switches the MegaROM ROM 0 on/off and will allow you to overlay the internal ROM 0.
Jumper 3 is used to to select whether a 1Mbit EPROM (8 Roms -> 0-7) or 2Mbit EPROM (16 ROMs -> 0-15) is installed on the board. If it's set to 1Mbit, but a 2Mbit is installed, it just hides the ROMs 8-15.

Rev. B. will have a fourth Jumper: Jumper 4 has two functions, if a 1Mbit EPROM is installed it selects whether the 8 ROMs have the numbers 0-7 or 8-15. If a 2Mbit EPROM is installed, it will allow you to hide ROMs 0-7 or 8-15 (when jumper 3 is set to 1Mbit EPROM).

Note on Jumper 1 and a question to the community: Several people have insisted that it is possible to overlay both the internal ROMs (0 and 7) on a STANDARD NON MODIFIED CPC6128 (Not the plus version, I know that can be overlayed). Although I can see how the hardware disables ROM 0 (using the ROMDIS signal), there is no hardware in the CPC that could possibly disable ROM 7. ROMDIS does not disable ROM 7. And all attempts I've made to block the internal ROM 7 from communicating have failed. The internal ROM 7 is wired parallel to the external one, so that if an image is put on the MegaROM in position 7, both ROM 7s (internal and MegaROM) answer in parallel. This means that I can't overlay the internal one with say ParaDOS because the AMSDOS and ParaDOS would answer in parallel on the data bus. It was claimed, that Inicron could do this, so I went to the bother of building the Inicron RamROM, but as I suspected, it can't, the internal ROM 7 still answers and the CPC crashes when ROM 7 is initialised. Can someone please prove me wrong? Is there a software trick/ firmware modification to achieve this? This would answer a question that has been bothering me (and others) for several weeks.

Bryce.

[redbox]

Being flash programmable directly from the CPC and being able to able to map into the CPC+ cart space would be the holy grail for Plus owners 

I'm assuming you could load 4 or more cart images into the mega rom and patch the Basic start-up to access them.

This is all very exciting...!

[CPCIak]

Well, in my opinion the ROMCard should be as cheap as possible. People who have know-how in electronics can modify the item to their needs themselves.

[Bryce]

If a cartridge replacement version is possible, then I'd make it as a different project, I wouldn't add cartridge functionality to the standard MegaROM for cost reasons.

Either way, I doubt I'll be able to make any CPC+ hardware without owning one. So until I get my hands on one, it's all theoretical for now anyway.

Bryce.

[eliot]

Being flash programmable directly from the CPC and being able to able to map into the CPC+ cart space would be the holy grail for Plus owners   I'm assuming you could load 4 or more cart images into the mega rom and patch the Basic start-up to access them. This is all very exciting...!

It already exists but it's rare!  http://www.cpcwiki.eu/index.php/RAM7_Cartridge_Hacker
It stores 4 games.

[redbox]

It already exists but it's rare! http://www.cpcwiki.eu/index.php/RAM7_Cartridge_Hacker
It stores 4 games.

I would love one of these...

But the MegaROM in either it's current incarnation or flashable would also be excellent. 

[steve]

This is pure guesswork, but I would think the plus cartridge slot uses rom numbers 0 to 31, so a plus romboard that connects to the expansion slot would have to use 32 to 47.

Or even 32 to 63 for 512k x 8 rom.

[TFM]

The CPC Plus cartridges use the ROM numbers &80, &81, &82 and so on...

Some of the ROMs are mapped in a second time at position 0 and 7.

So if you want to make a cart-simulator, use &80... and ascending.

[arnoldemu]

Note on Jumper 1 and a question to the community: Several people have insisted that it is possible to overlay both the internal ROMs (0 and 7) on a STANDARD NON MODIFIED CPC6128 (Not the plus version, I know that can be overlayed). Although I can see how the hardware disables ROM 0 (using the ROMDIS signal), there is no hardware in the CPC that could possibly disable ROM 7. ROMDIS does not disable ROM 7. And all attempts I've made to block the internal ROM 7 from communicating have failed. The internal ROM 7 is wired parallel to the external one, so that if an image is put on the MegaROM in position 7, both ROM 7s (internal and MegaROM) answer in parallel. This means that I can't overlay the internal one with say ParaDOS because the AMSDOS and ParaDOS would answer in parallel on the data bus. It was claimed, that Inicron could do this, so I went to the bother of building the Inicron RamROM, but as I suspected, it can't, the internal ROM 7 still answers and the CPC crashes when ROM 7 is initialised. Can someone please prove me wrong? Is there a software trick/ firmware modification to achieve this? This would answer a question that has been bothering me (and others) for several weeks.

Bryce.

Would it respond to /exp and make itself rom 0?
So you could in effect remap it and then yours takes position 7?
Extra logic yes, so that when slot 7 is activated, /exp goes low to remap amsdos, then your rom responds and can be read?

[Bryce]

Hi Arnoldemu,
         Good suggestion, but I investigated that already, the answer is no unfortunately. EXP is hardwired to GND in the 6128. I assume Amstrad intended to use that signal so that software could detect whether a disk drive is attached or not. On the 464 EXP is normally high (pulled high by R104) and gets pulled low by the DDI-1 (and possibly by other external drives too). Port B5 of the PIO can be read to detect whether a drive is connected or not.

Bryce.

Edit: Also, the devices that allegedly can replace ROM 7 (Inicron RamRom and SFII) don't connect to this pin either.

[pepax]

Still, really, and I propose this for the community, if someone with a burner could provide a burning service, like the magazine DVDs I've been sending out, this would be sweet...

Here's your free flash ROM burner.  It's actually the SMC 1211TX-WL50 network card + a ZIF socket + a switch (The card itself can't program flash ROMs larger than 1Mbit and I needed to program 2Mbit ones  )
http://www.flickr.com/photos/93402213@N00/680353911/
Beware - the 1211TX without the WL50 suffix have 28-pin DIP sockets only!
The Linux software can be found here: http://ctflasher.sourceforge.net/
And the free 1 or 2Mbit DIP flash ROMs can be found in most discarded old PCs (which makes them useful at last  ).

[pepax]

TFM are you planning to produce the MegaROM PCBs anytime soon? I'd love to buy a few bare ones, along with one ACID chip. 

[Gryzor]

Here's your free flash ROM burner.  It's actually the SMC 1211TX-WL50 network card + a ZIF socket + a switch (The card itself can't program flash ROMs larger than 1Mbit and I needed to program 2Mbit ones  )
http://www.flickr.com/photos/93402213@N00/680353911/
Beware - the 1211TX without the WL50 suffix have 28-pin DIP sockets only!
The Linux software can be found here: http://ctflasher.sourceforge.net/
And the free 1 or 2Mbit DIP flash ROMs can be found in most discarded old PCs (which makes them useful at last  ).

So... um, wait, does this mean you're giving it away??? If so I'd gladly do the service to the community...

[pepax]

So... um, wait, does this mean you're giving it away??? If so I'd gladly do the service to the community...

Nope, it means that you can easily find this particular network card in a junkyard and make yourself a flash ROM programmer.
But if you press hard enough, I may be willing to send you one of these cards, I've found quite a lot of them in junk over the years.....  The 40pin ZIF socket was on sale, cheaper than a 32pin one (that explains a lot  ), I may still have some left.

[redbox]

And the free 1 or 2Mbit DIP flash ROMs can be found in most discarded old PCs (which makes them useful at last  ).

Or you could use the motherboard's (that you're pulling the ROMs from) flashing utility and do it that way?

That's what I'm planning on, but haven't actually tried it yet 

[Bryce]

You'd have to remove the BIOS on the motherboard though??? Then it won't boot anymore, so that probably won't work unless you have one of those fancy motherboards that try to pull the BIOS image from CD / USB stick automatically. Way too much trouble. Buy a cheap EPROM burner or build one, if you need to program EPROMs / Flash regularly.

Bryce.

[pepax]

You'd have to remove the BIOS on the motherboard though??? Then it won't boot anymore, so that probably won't work unless you have one of those fancy motherboards that try to pull the BIOS image from CD / USB stick automatically. Way too much trouble. Buy a cheap EPROM burner or build one, if you need to program EPROMs / Flash regularly.

Bryce.

Yes, you'd have to pull the BIOS, after the PC has already booted up.    It's called hot swapping, isn't it? AFAIK the PC may or may not like it. 

[TFM]

TFM are you planning to produce the MegaROM PCBs anytime soon? I'd love to buy a few bare ones, along with one ACID chip. 

Well, if I can manage it, then I will get them in my fingers not before the end of december. No need to wait for me.

[Gryzor]

I've pulled BIOS chips off mobos in the past with no problem, really (in order to program another one from a mobo with problems usually) and never had any issues...

But anyhow, since 'cheap' was mentioned, can someone suggest one?

[Bryce]

Like most things in life, cheap is relative, but if you really think you have use for an EPROM / Flash burner, that can burn almost any chip you'll ever come across, then I would definitely recommend the BX32 Batupo from Batronix:

http://www.progshop.com/shop/programmer/BX32/eprom-programmer.html

I've seen it on offer for under 100€ elsewhere, it doesn't need a powersupply (takes it's power from USB), it can burn almost everything you'll ever need to program (about 10,000 different types of IC at the moment)

http://www.progshop.com/pdf/BX32DeviceList.pdf

and it's a really well built robust unit. There's also no dip-switches or settings needed, the unit will auto-detect the chip inserted. I personally use a BX40 and BX48, which cost quite a but more, but offer extra functions, that most 8-bit users won't require.

Bryce.

[Gryzor]

Yup, that's the one we discussed about in PMs as well. But, unfortunately, I can't see myself burning lots of EPROMs so €100 is a tad on the high side

There's a flood of EPROM programmers on eBay, but I wouldn't really know which one would be suitable for our needs. For instance, how about this ?