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Disable ROM 7 DOS on 6128

Started by Squeekboxandj, 09:22, 09 December 22

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Squeekboxandj

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CPC464 & 6128

GUNHED

Quote from: Bryce on 10:55, 11 December 22
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.

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.  :)
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pelrun

There is no need to disconnect R211 at all. Just add the switch to ground.

zhulien

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?

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?

How do you know that it does? They have identical content and the same ROM number.

Bryce.

eto

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?

zhulien

Quote from: eto on 15:51, 18 December 22
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?
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.

gerald

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.

zhulien

I was thinking it might be similar to having the 256k memory expansion in a 6128, i still get only 320k ram

eto

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. 

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