MEGAFLASH interface

[IanS]

Alright. To be at the safe side I leave all like it is and the user has to switch on ROM 0. And why not? It usually contains a copy of the real ROM 0 (or an advanced version). So no reason to keep it OFF.

However I may add a 'Flash-manufacturer ID recognizer' one day and then this knowledge may be beneficial.

The 39sf040 works in similar way, it's what I do with my flash rom board. (The data sheet says that the address is only read from A0-A14 and that A15-A19 need to be all 1 or all 0, but that doesn't seem to be the case on chips I've tried).

I don't think the megaflash design supports reading the Flash-ID, as you can't read from the flash chip when in write mode.

[TFM]

Oh, well, I have to find out with real hardware. They told me before that the CPC can't switch the SDP on or off, and now ROManager can do it. So maybe there is a way.

[Gryzor]

Me likey. Very tidy, and a substantial improvement if you only use MegaFlash!

[wilco2009]

After some time working with my Megaflash interface I have found a very curious problem.
Firstly I had copied, internal AMSDOS ROM to ROM7 and everything has been working right until now.
Yesterday I tried to install a diferent Disk OS in ROM7. I tryied with RODOS first and AMDOS 0.7 after, and I get a corrupt name in ROM7 and a non working Disk OS ROM.
If I read the content of the flash memory with my EPROM programmer the content of the ROM7 match exactly with the file copied (RODOS or AMSDOS 0.7).


Due to it, I know my interface is working right writing ROM7, then it have to be not working reading ROM7.
By other hand, if I copy internal ROM to ROM7 then my Megaflash works right. Due to it, I think the CPC is reading partially internal ROM and partially ROM7, mixing the content.


Additionally, all other ROMs (including ROM0) are working right in reading and writting.


I was measuring continuity comparing with the schema, and I was comparing my schema with Bryce schema and everithing seems correct. (Of course something is wrong)


Somebody could have some idea about what could be the problem?

[gerald]

This is expected 
On  a 6128/664 or 464+DDI1, ROM 7 cannot be masked by an external rom expansion without a HW modification on the CPC (or DDI1).
More there : Disabling ROM 7

[wilco2009]

Thanks a lot. You have saved me a lot of hours with the multimeter. 

[IanS]

This is expected 
On  a 6128/664 or 464+DDI1, ROM 7 cannot be masked by an external rom expansion without a HW modification on the CPC (or DDI1).
More there : Disabling ROM 7

Disabling the internal disk rom also discissed here - Disable Disc ROM

Basically linking pin 13 (or any of the connected tracks ) of IC210 to GND will stop the internal rom from ever being selected.

[TotO]

With a big 512K ROM board, what is the interest to disabling ROM7?
Putting PARADOS on ROM6 and it's done. No?

[wilco2009]

Yes, but I tried to put ROMDOS for example.
I'm a newbie in CPC matters and I'm not sure if I'll need to patch ROM7 in any case.

[TotO]

I have never tried ROMDOS. It not work in ROM6?

[wilco2009]

No it doesn't.There are a lot of DOS ROMS only working on ROM7. See ROM List - CPCWiki

[TFM]

Enhanced DOS ROMs working fine at positions 2-7 (1 shall be reserved for the RAMdisc ROM RDOS from Dobbertin) are VDOS and X-DDOS and probably others.