symbiface 2 rom switches

[arnoldemu]

I will eventually find the answer, but I was wondering:

- can symbiface 2 override rom 7?
- can symbiface 2 override rom 0?
- rom switches are numbered 1-8 which seems to be for disabling roms 1-8?
- how is it possible to disable roms 8-31 using switches? Not possible?
- what is j2 for?

[TFM]

That's what happens with my SF2 (some will disagree, but forget it, better more than less, right?)


- It can overwrite ROM 0
- It can overwrite ROM 7
- ROM switches are numbered 0-7 to switch ON/OFF ROMs 0-7


- (There is a switch to disable ALL ROM IIRC.)

[arnoldemu]

That's what happens with my SF2 (some will disagree, but forget it, better more than less, right?)


- It can overwrite ROM 0
- It can overwrite ROM 7
- ROM switches are numbered 0-7 to switch ON/OFF ROMs 0-7


- (There is a switch to disable ALL ROM IIRC.)

Yes I see it can overwrite rom 0.
Rom 7 it's a bit strange with my test...

j2 seems to control programming roms 8-31. If j2 is present, then only roms 0-7 can be activated, if j2 is missing then I think roms 0-31 are accessible.
I need to do more testing.

[TFM]

Well, ROM 7 can be replaced, yes. But not with all CPCs, because they got different PCBs. I would suggest to enable the ROM 7 replacement, because it works on most CPC and the Plus.


Are you going to also emulate ROM writing? Only asking out of curiosity, it may be not needed though.

[arnoldemu]

Well, ROM 7 can be replaced, yes. But not with all CPCs, because they got different PCBs. I would suggest to enable the ROM 7 replacement, because it works on most CPC and the Plus.

I already emulate the rom 7 overwrite on Plus. On CPC it is not emulated so that it is the same as some of the PCBs.
I will add it as a setting on CPC too.

Are you going to also emulate ROM writing? Only asking out of curiosity, it may be not needed though.

Yes. The ROM data will be saved with the settings. So in this way I emulate the battery protection

[TFM]

I already emulate the rom 7 overwrite on Plus. On CPC it is not emulated so that it is the same as some of the PCBs.
I will add it as a setting on CPC too.

That's great since all my CPC6128 can replace ROM 7 using an SF2 or similar. 

Yes. The ROM data will be saved with the settings. So in this way I emulate the battery protection

Hmm. Sorry, I wasn't clear. Can I use my ROManager to write to the ROMs of the SF2 - like on a real CPC?
(I'm just asking, because it could help development, but I guess it would also be too much effort to implement that).

[arnoldemu]

That's great since all my CPC6128 can replace ROM 7 using an SF2 or similar. 

Hmm. Sorry, I wasn't clear. Can I use my ROManager to write to the ROMs of the SF2 - like on a real CPC?
(I'm just asking, because it could help development, but I guess it would also be too much effort to implement that).

Yes you were clear. Yes you will be able to use your ROMManager to write the ROMs on the emulated sf2.

[TFM]

Yes you were clear. Yes you will be able to use your ROMManager to write the ROMs on the emulated sf2.

Very nice, but it's called ... ROManager (c) - with one big M only. 


Really looking forward to the next update. 

[Bryce]

I have tried over-writing on every CPC664 / 6128 that I have fixed in the last few years (and it was many). I haven't found a non-plus CPC yet that allows ROM 7 to be over-written reliably. If it does happen it's pure luck. Electronically it shouldn't be possible. The connections just don't exist.

Bryce.

[TFM]

I have tried over-writing on every CPC664 / 6128 that I have fixed in the last few years (and it was many). I haven't found a non-plus CPC yet that allows ROM 7 to be over-written reliably. If it does happen it's pure luck. Electronically it shouldn't be possible. The connections just don't exist.

Bryce.

It was just a question of time until you show up with this again. Do we really need another round of this discussion? I bet you $1000 that it works with 3 of my CPC6128 computers just to end this topic once and for ever.

[Bryce]

I don't intend discussing it, or placing any bets. I'm just stating what my experience is. The electronic side of it can be confirmed by several other members here. That's not an opinion, it's a fact.

Bryce.

[TFM]

I don't intend discussing it, or placing any bets. I'm just stating what my experience is. The electronic side of it can be confirmed by several other members here. That's not an opinion, it's a fact.

Bryce.

Sure! 

[robcfg]

I guess you don't have the three machines at hand, but just in case, it would be nice to check the boards MCxxx code.


Just saying... 

[Grim]

I haven't found a non-plus CPC yet that allows ROM 7 to be over-written reliably. If it does happen it's pure luck. Electronically it shouldn't be possible. The connections just don't exist.

+1

I also would be interested in seeing pictures of theses motherboards to maybe find out new elements that could explain their unusual behavior.

[gerald]

+1

I also would be interested in seeing pictures of theses motherboards to maybe find out new elements that could explain their unusual behavior.

These motherboard are like all other. They do not support external ROM7 by design. The only explanation explanation is a ROM IC drive strength in favor of the external one during read for the working one, and the opposite for non working ones.
But TFM is more a believer than a scientist on this case, and he will stick to his theory : AMSTRAD designed his CPCs so you can disable ROM7.
Just a scope probe on data lines of the data bus during a ROM read will tell us.

[Munchausen]

I don't intend discussing it, or placing any bets. I'm just stating what my experience is. The electronic side of it can be confirmed by several other members here. That's not an opinion, it's a fact.

Bryce.

I have three CPC 6128s. One of them can have ROM7 overridden in this way, and it is reliable - it works every single time. I was actually confused when it didn't work on my other machines, and thought something was wrong with them until I checked the forums. I'm not saying it works by design, but it does work. I'd be happy to take a video of me doing this, or do whatever tests you want with a scope, but not until mid February because I'm snowed under with work until then and my CPCs and scope are in the garage.

[Bryce]

Yeah, I'd like to see that. Do you know whether it happens to be one that has the Pre-ASIC inside?

Bryce.

[Munchausen]

Yeah, I'd like to see that. Do you know whether it happens to be one that has the Pre-ASIC inside?

Bryce.

None of them have a pre-ASIC, two have 40010 and the other a 40007. The one that it works on has a 40010.

[gerald]

Yeah, I'd like to see that. Do you know whether it happens to be one that has the Pre-ASIC inside?

Preasic does not allow internal ROM7 disabling either.
Details here : Arnold4 - CPCWiki

None of them have a pre-ASIC, two have 40010 and the other a 40007. The one that it works on has a 40010.

The GA is not involved in the ROM selection. On a regular CPC (ie non plus or pre-asic), the ROM disable mechanism is just driving high a pull down resistor on the CS of the main ROM (FW/BASIC). The ROM7 selection circuit does the same and is NOT inhibited by ROMDIS.
Discussed here : Disabling ROM 7

[Munchausen]

Preasic does not allow internal ROM7 disabling either.
Details here : Arnold4 - CPCWiki
The GA is not involved in the ROM selection. On a regular CPC (ie non plus or pre-asic), the ROM disable mechanism is just driving high a pull down resistor on the CS of the main ROM (FW/BASIC). The ROM7 selection circuit does the same and is NOT inhibited by ROMDIS.
Discussed here : Disabling ROM 7

I know. This was simply to give some information about which version of mainboard they are using, it's what I remember - I don't know the mainboard version numbers off of the top of my head but I can remember this.

EDIT: From your linked thread (where we discussed this before) I now know the one it works on is an MC0020C

[arnoldemu]

None of them have a pre-ASIC, two have 40010 and the other a 40007. The one that it works on has a 40010.

Please take a photo of the pcb on both sides.
I'll think if there is a way I can write a test that can show it up.

Perhaps your CPC also shows the bus value strangeness that @SyX reported?

[arnoldemu]

My original post wasn't to start this conversation again, although it would be good to finally give an explanation of what is happening, but it was to ask if the Symbiface 2 allowed the user to define a rom 7 replacement.

[arnoldemu]

Very nice, but it's called ... ROManager (c) - with one big M only. 


Really looking forward to the next update. 

You will be able to use both ROManager (c) and ROMManager  

[gerald]

I know. This was simply to give some information about which version of mainboard they are using, it's what I remember - I don't know the mainboard version numbers off of the top of my head but I can remember this.

EDIT: From your linked thread (where we discussed this before) I now know the one it works on is an MC0020C

The component involved are :
The internal ROM
The external ROM (RAM in the case of symbiface)
The Z80

Both ROM will drive the data bus at the same time : 0+0 = 0, 1+1= 1, 1+0 =x, 0+1=y.
Then the Z80 input level caracteristics will decide if x and y mean 0 or 1.

So reference of all these 3 component are more important than the board revision.

My original post wasn't to start this conversation again, although it would be good to finally give an explanation of what is happening

This had to happen
I am 99% sure of my explanation. Send me a "working" set of CPC/symbiface and I will confirm it. A symbiface alone may be enough.

End of thread derailing for me.

[Munchausen]

The component involved are :
The internal ROM
The external ROM (RAM in the case of symbiface)
The Z80

Both ROM will drive the data bus at the same time : 0+0 = 0, 1+1= 1, 1+0 =x, 0+1=y.
Then the Z80 input level caracteristics will decide if x and y mean 0 or 1.

So reference of all these 3 component are more important than the board revision.
This had to happen
I am 99% sure of my explanation. Send me a "working" set of CPC/symbiface and I will confirm it. A symbiface alone may be enough.

End of thread derailing for me.

I suspect that you are right and there is no difference in the parts, but just a manufacturing tolerance with an unforeseen side effect. As well as the symbiface I also have an XS-Mem I can test it with. I'll make a new thread when I get it out to test...