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Disable ROM 7 DOS on 6128

Started by Squeekboxandj, 09:22, 09 December 22

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Squeekboxandj

Hello to you all.

I wanted to know what is the latest preferred way to disable a 6128 ROM 7 AMSDOS so that I can use a ROM expansion board with ROM 7 capabilities and install another DOS like Parados or UniDos.

At the moment I was thinking of using either Iconsgr 512Kb rom board or TotO's Dual Rom board but I'm open to other ideas. 

My 6128 board is MC0020I

I was reading on the Forum about placing a switch to ground R211 at pin 10 on IC210 (74LS132). Is this still the best option, only seems a bit barbaric in 2022!

Thanks in advance for any help. 
CPC464 & 6128

abalore

You can also use my Plus2CPC or Play2CPC boards and load a different Firmware/BASIC/DOS from cartridge, and also you'll have cartridge support in your CPC ;)

eto

Quote from: abalore on 12:02, 09 December 22You can also use my Plus2CPC or Play2CPC boards and load a different Firmware/BASIC/DOS from cartridge, and also you'll have cartridge support in your CPC ;)
how does it disable ROM 7? I thought the logic to select ROM 7 is baked into the circuits and can't be overridden from outside on a normal CPC?! At least not without modification.

TotO

#3
The ROM7 should never need direct replacement. But if a day I had no choice, I would replace the motherboard circuit with another (on socket) but never a dirty hack by cutting a track. The main issue is software, not hardware.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

eto

Quote from: TotO on 12:26, 09 December 22The ROM7 should never need direct replacement. But if a day I had no choice, I would replace the motherboard circuit with another (on socket) but never a dirty hack by cutting a track. The main issue is software, not hardware.
Squeekboxandj asked for that. I was just curious how Plus2CPC would allow an external ROM to override the internal AMSDOS after Abalore mentioned that you can load a different DOS. 

TotO

#5
Quote from: eto on 12:47, 09 December 22I was just curious how Plus2CPC would allow an external ROM to override the internal AMSDOS
I think he just answer about what extra ROM devices can be used today like D-ROM, ... (not related to the 6128 limitation).
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

GUNHED

Most of the CPC6128 in Germany are able to allow to switch off the internal ROM 7 from the outside. So any kind of ROM box can have a ROM 7 and this will work just fine.

However, few CPC6128 in Germany are not capable of replacing ROM 7 by using an ROM expansion. The degree of non working CPCs seem to be higher in the non-German CPC-population.

Conclusion: Try and test if ROM 7 can be replaced in your case (you can do this with M4 expansion, FlashGordon, MegaFlash - anything which provides ROM 7 externally).
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eto

Quote from: GUNHED on 13:54, 09 December 22Most of the CPC6128 in Germany are able to allow to switch off the internal ROM 7 from the outside. So any kind of ROM box can have a ROM 7 and this will work just fine.
what's the different of them?

TotO

@eto Bus contention... Nothing special, I don't know why GUNHED (previously TFM) said again that.
All about the discution here: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/disabling-rom-7/
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

GUNHED

Quote from: eto on 14:07, 09 December 22
Quote from: GUNHED on 13:54, 09 December 22Most of the CPC6128 in Germany are able to allow to switch off the internal ROM 7 from the outside. So any kind of ROM box can have a ROM 7 and this will work just fine.
what's the different of them?
The mainboards are different
http://futureos.de --> Get the revolutionary FutureOS (Update: 2023.11.30)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

GUNHED

Quote from: TotO on 14:38, 09 December 22@eto Bus contention... Nothing special, I don't know why GUNHED (previously TFM) said again that.
All about the discution here: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/disabling-rom-7/

What a strange question. I told it because that's the topic of this post. And I tried to answer the question of the user (see 1st post).

And yes previously TFM. So give me my nick back!
http://futureos.de --> Get the revolutionary FutureOS (Update: 2023.11.30)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

TotO

#11
Quote from: GUNHED on 14:52, 09 December 22What a strange question. I told it because that's the topic of this post. And I tried to answer the question of the user (see 1st post).
But you know that your answer is false, because the reason was explain to the link I have pointed, where you have participated.  It is an undesired side effect of the electronic done by a concurent bus driving. The final issue can be sad.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

GUNHED

Well, if you want to be right.... then....  YES - YOU'RE RIGHT - AND I'M ALL WRONG!!!

Hope you feel better now.  ;D
http://futureos.de --> Get the revolutionary FutureOS (Update: 2023.11.30)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

TotO

Quote from: GUNHED on 15:05, 09 December 22Well, if you want to be right.... then....  YES - YOU'RE RIGHT - AND I'M ALL WRONG!!!

Hope you feel better now.  ;D
I don't want to be right, but that you stop to be wrong. :-*
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

pelrun

#14
"The mainboards are different" not in any meaningful way - and I say this as the guy who actually did all the work to fully document it (https://raw.githubusercontent.com/pelrun/cpc-schematics/master/cpc6128/outputs/mc0020x-sch.pdf). Even though the circuit is integrated into the mainboard it still acts like an external rom box and only drives ROMDIS, it doesn't read it. If anything else tries to drive the bus as ROM 7 it is guaranteed to fight the outputs of the internal disk ROM.

Forcing bus contention and expecting to win out is the crappiest way to make a design work; it is only through dumb luck that GUNHED hasn't burned out a chip. Sure, it might work sometimes, but every time you do it is a risk and it shouldn't be recommended to others.

Putting a switch between ground and R211 is actually the cleanest way to do it. IC210's outputs are open collector and can only pull low, which is why they can be safely connected together; either they're all high impedance and R211 can pull the output high, or one or more is pulling low and the output is low. An extra switch to ground is perfectly legal!

The interesting thing is the other side of IC210. Each XOR gate has D0,D1 or D2 on one input and /EXP on the other, but /EXP is pulled hard to ground via LK7, essentially making /EXP useless and turning IC210 into a simple buffer. If you cut LK7 then /EXP gets pulled high and the amsdos rom moves to ROM 0. ???

(That /EXP is connected there is really, really bugging me now. I have to go check to see if that's actually true or if there's an error in my schematics...)

eto

Quote from: TotO on 14:38, 09 December 22@eto Bus contention... Nothing special, I don't know why GUNHED (previously TFM) said again that.
All about the discution here: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/disabling-rom-7/

Ok, my understanding so far: so some boards really support it, in others it's just a side effect.

Is the side effect reliable or more "results may vary" kind of thing?

TotO

#16
No, all the "DDI" (internal or external) use the same schematic and the ROM7 was not designed to be disabled. The only way to see it working is to answer faster than the internal one and won the bus contention... A good way to do is to put the new DOS at ROM6 and patch the few ROM that are hardcoded to access the ROM7.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

GUNHED

Quote from: TotO on 15:21, 09 December 22
Quote from: GUNHED on 15:05, 09 December 22Well, if you want to be right.... then....  YES - YOU'RE RIGHT - AND I'M ALL WRONG!!!

Hope you feel better now.  ;D
I don't want to be right, but that you stop to be wrong. :-*
Easy! Stop to misunderstand me  :)
http://futureos.de --> Get the revolutionary FutureOS (Update: 2023.11.30)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

rpalmer

If people are game, the best solution is to de-solder the ROM, solder in a socket and return ROM into socket (or program a new one of your DOS of choice).
This something I did and have not looked back and It also allows me to have a ROM board with a ROM 7 in which I could make it possible to change the ROM with the need to open up the CPC.

rpalmer

abalore

#19
Quote from: eto on 12:05, 09 December 22
Quote from: abalore on 12:02, 09 December 22You can also use my Plus2CPC or Play2CPC boards and load a different Firmware/BASIC/DOS from cartridge, and also you'll have cartridge support in your CPC ;)
how does it disable ROM 7? I thought the logic to select ROM 7 is baked into the circuits and can't be overridden from outside on a normal CPC?! At least not without modification.
with a patched firmware that doesn't initialize ROM 7 and sets the DOS to another slot, like 6. As I said, in the cartridge you need to replace firmware, BASIC and AMSDOS

abalore

Quote from: TotO on 18:16, 09 December 22No, all the "DDI" (internal or external) use the same schematic and the ROM7 was not designed to be disabled. The only way to see it working is to answer faster than the internal one and won the bus contention... A good way to do is to put the new DOS at ROM6 and patch the few ROM that are hardcoded to access the ROM7.

now I see you said it before

GUNHED

Quote from: eto on 15:47, 09 December 22
Quote from: TotO on 14:38, 09 December 22@eto Bus contention... Nothing special, I don't know why GUNHED (previously TFM) said again that.
All about the discution here: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/disabling-rom-7/

Ok, my understanding so far: so some boards really support it, in others it's just a side effect.

Is the side effect reliable or more "results may vary" kind of thing?
It's 100% reliable, if it works if works all the time (if not then never).  :)
http://futureos.de --> Get the revolutionary FutureOS (Update: 2023.11.30)
http://futureos.cpc-live.com/files/LambdaSpeak_RSX_by_TFM.zip --> Get the RSX-ROM for LambdaSpeak :-) (Updated: 2021.12.26)

Bryce

Quote from: GUNHED on 02:37, 11 December 22
Quote from: eto on 15:47, 09 December 22
Quote from: TotO on 14:38, 09 December 22@eto Bus contention... Nothing special, I don't know why GUNHED (previously TFM) said again that.
All about the discution here: https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/disabling-rom-7/

Ok, my understanding so far: so some boards really support it, in others it's just a side effect.

Is the side effect reliable or more "results may vary" kind of thing?
It's 100% reliable, if it works if works all the time (if not then never).  :)

The reliability is not what's being questioned. It's the fact that when it does work, you are forcing an IC into a situation which is not recommended for the component. The component is being used outside its limits, so you are risking damaging the CPC. It may work fine for a long time without an issue, but it might also fail and you'll be left with a non-working CPC.

Bryce.

Squeekboxandj

Thank you for your replies. 

I've pasted Bryce's picture above (from the earlier 2013 Wiki post) that physically disables ROM7. 

I wanted to ensure my understanding is correct. 

The switch should be placed BETWEEN R211 and pin 10 of IC210 (74LS132),

And, the purpose of the switch is to disconnect R211 and simultaneously ground pin 10 of IC210. 

Many thanks
CPC464 & 6128

Squeekboxandj

CPC464 & 6128

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