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.
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 ;)
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.
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.
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.
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).
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).
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?
@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/
Quote from: eto on 14:07, 09 December 22Quote 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
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!
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.
Well, if you want to be right.... then.... YES - YOU'RE RIGHT - AND I'M ALL WRONG!!!
Hope you feel better now. ;D
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. :-*
"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...)
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?
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.
Quote from: TotO on 15:21, 09 December 22Quote 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 :)
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
Quote from: eto on 12:05, 09 December 22Quote 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
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
Quote from: eto on 15:47, 09 December 22Quote 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). :)
Quote from: GUNHED on 02:37, 11 December 22Quote from: eto on 15:47, 09 December 22Quote 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.
(about:invalid)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
(about:invalid)
dlattach.png
Quote from: Bryce on 10:55, 11 December 22Quote from: GUNHED on 02:37, 11 December 22Quote from: eto on 15:47, 09 December 22Quote 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.
Well, you are more into electronics than me for sure. All I do is to tell about my personal experiences. I got my first EPROM box back the day around 1990 or late 80ies. It already provided the possibility to replace ROM number 7. So the producer was not scared about using it and they are for sure electronic experts too (the company did lots of 100% reliable expansions for CPC and does still flourish on electronics market).
However I leave that (hardware) discussion to the experts.
From experience I can tell that since over 30 years no CPC or 6128plus ever died in my hands. And ROM 7 was always controlled from a outside (EP)ROM / Flash-ROM box. There was never a problem (timg issues of Plus vs. CPC are a different topic). So according to my opinion I'm sure it's save. :)
There is no need to disconnect R211 at all. Just add the switch to ground.
on a 664, if I plug in the DD-1 controller, the DD-1 ROM 7 takes over the internal one - does it not do that on a 6128?
Quote from: zhulien on 15:39, 18 December 22on a 664, if I plug in the DD-1 controller, the DD-1 ROM 7 takes over the internal one - does it not do that on a 6128?
How do you know that it does? They have identical content and the same ROM number.
Bryce.
Quote from: zhulien on 15:39, 18 December 22on a 664, if I plug in the DD-1 controller, the DD-1 ROM 7 takes over the internal one - does it not do that on a 6128?
when would someone connect a DDI to a 664 or 6128?
Quote from: eto on 15:51, 18 December 22Quote from: zhulien on 15:39, 18 December 22on a 664, if I plug in the DD-1 controller, the DD-1 ROM 7 takes over the internal one - does it not do that on a 6128?
when would someone connect a DDI to a 664 or 6128?
when you want to easily change the ROM in the DD1 box instead of inside the CPC - which is what we did - we cut a hole in the DD1 slot back in the day to allow for 2 ROMS to be piggy backed so we didn't have to modify the 664. As I didn't actually do the mod at the time, I am unsure if anything else was done other than the hole and the piggy backed ROMs + switch - but I don't think anything else was done.
Quote from: zhulien on 18:00, 18 December 22when you want to easily change the ROM in the DD1 box instead of inside the CPC - which is what we did - we cut a hole in the DD1 slot back in the day to allow for 2 ROMS to be piggy backed so we didn't have to modify the 664. As I didn't actually do the mod at the time, I am unsure if anything else was done other than the hole and the piggy backed ROMs + switch - but I don't think anything else was done.
Since the FDC in the 664/6128 are using the same IO port as the DDI one, I think your mod also included a FDC disconnection of some sort, or it wouldn't work at all.
I was thinking it might be similar to having the 256k memory expansion in a 6128, i still get only 320k ram
Quote from: zhulien on 13:40, 19 December 22I was thinking it might be similar to having the 256k memory expansion in a 6128, i still get only 320k ram
Similar, but not identical
- the external RAM usually will set the RAMDIS signal which disables the internal RAM
- An external ROM will set the ROMDIS signal but which disables lower ROM but not ROM 7.
It's like you would have two ROMs in an external ROM box and both are set to ROM 7.