Disabling ROM 7

[Bryce]

Do these programs do it directly or use Firmware calls to initialise the ROM. If they use the Firmware, then you could re-direct the calls to ROM 7 to the new ROM number?

The LowerROM isn't really disabling ROM 7, it's only inhibiting the initialisation. So if an external ROM 7 is initialised, then the internal ROM 7 will be answering the requests to the external ROM 7 in parallel. So the external ROM 7 still couldn't be an alternative version, it would have to be an exact copy of AMSDOS.

Bryce.

[TFM]

Forget it, most games bank in ROM7 and use routines of ROM7. Some may use the firmware, but most do it directly.

Why don't you try it by yourself? Move AMSDOS from ROM 7 to ROM 5 (for example) and see how much game are still running. No, don't take all that cracked games, take original stuff.    And for Apps. check OCP art studio. 

[wilco2009]

If I have understood right, to be able to patch ROM7 with MEGAflash is necessary to set pin 20 or pin 22 of internal AMSDOS ROM to 5v. Isn't it?


There are not another way?

[IanS]

If I have understood right, to be able to patch ROM7 with MEGAflash is necessary to set pin 20 or pin 22 of internal AMSDOS ROM to 5v. Isn't it?


There are not another way?

Pin 20 or 22 to 5V is not a good idea. Connecting anything directly to 5V is generally not recommended (especially if you aren't sure).

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

[Bryce]

As IanS says, don't directly connect either of these pins to 5V. The best way to do it is to add a switch that disconnects pin20 from the pcb and instead connects it to 5V via a 10K resistor. This will allow you to enable/disable ROM7 when you wish. See attachment.

Bryce.

[wilco2009]

Pin 20 or 22 to 5V is not a good idea. Connecting anything directly to 5V is generally not recommended (especially if you aren't sure).

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

[/size]

As IanS says, don't directly connect either of these pins to 5V. The best way to do it is to add a switch that disconnects pin20 from the pcb and instead connects it to 5V via a 10K resistor. This will allow you to enable/disable ROM7 when you wish. See attachment.

Bryce.


[/size]

 


Thanks to both.


I'll try with the selector option.

[IanS]

As IanS says, don't directly connect either of these pins to 5V. The best way to do it is to add a switch that disconnects pin20 from the pcb and instead connects it to 5V via a 10K resistor. This will allow you to enable/disable ROM7 when you wish. See attachment.

[/size][size=78%]
Why do you suggest cutting a pin when you can just attach two wires.
Linking pin 13 (or any of the connected tracks ) of IC210 to GND (via a switch) will stop the internal rom from ever being selected. No permanent damage required.[/size]

[Bryce]

Just because I prefer to do things they way I was taught. Your solution would have been considered bad practice at least the way we learnt it back then. That's not saying your solution doesn't work or isn't good. It's just not the way we were taught it back then.
Pulling pin 13 low means you are holding all the ouputs of the 74LS136 low. I know they are open collector, so it won't damage them or anything, but you are also permanently dropping 5V across R211. Ok, it's only going to pull 5mA[nb]In the type of commercial electronics I usually design, you'd be fired for knowingly "wasting" 5mA[/nb] or so, but it's not good practice. Of course cutting a pin isn't exactly good practice either, but from a schematic point of view I prefer to do it this way.

To use your way and make it more "Fussy bastard Bryce compatible" , I'd suggest removing R211 as well as adding your link.

Bryce.

Edit: Here's a suggestion that uses your pin 13 solution, doesn't involve cutting any pins, makes it switchable and removes the 5mA loss across R211.

[wilco2009]

Thanks again, I try this last solution. 
Easy and clear.

[IanS]

To use your way and make it more "Fussy bastard Bryce compatible" , I'd suggest removing R211 as well as adding your link.

Edit: Here's a suggestion that uses your pin 13 solution, doesn't involve cutting any pins, makes it switchable and removes the 5mA loss across R211.

The 5ma is being "wasted" whenever Rom 7 isn't enabled now, so I don't think it's a big deal. My method has the advantage that you only require 2 wires for the switch.

[Bryce]

Yeah, but I'm an over pedantic perfectionist. And my day job involves "worrying" about lost µAs, so to me it seems like a lot. All three versions are good solutions and work fine, it's up to the modder to decide which solution he/she prefers.

Bryce.

[TFM]

According to Flynn perfection can't be reached... but we can reach out for it! And I like that 

[Bryce]

Who's Flynn?

Bryce.

[redbox]

Who's Flynn?

Tron.

Nerdus maximus.

[TFM]

No, Tron Legacy...


so just 'junior' nerd 

[Bryce]

Ah, ok. I thought you meant this one: Flynn - CPCWiki

Bryce.

[TFM]

... an obvious reason for choosing a pseudo 

[wilco2009]

Ouch!, my 6128 not match with the schematics.


Pin 13 of IC210 is not connected with R211 in any side, and seems to be not used.

I think the best way in my case is to use the first solution proposed by Bryce. The function of pin 20 in a ROM is known and sure.

[Munchausen]

To add more confusion (or clarity?) to this topic - I have two 6128s here, one of them (an MC0020C) gets the ROM 7 disabled when you connect the LowerROM, the other (an MC0020I) does not.


There seem to be advantages & disadvantages to both - with ROM 7 disabled, you can add an external ROM7 of your choosing, but if you don't then you have a basically have an unusable CPC. Without it disabled, you can use the CPC without a ROM board, but you can't replace ROM 7  without hacking the CPC.

[TFM]

To add more confusion (or clarity?) to this topic - I have two 6128s here, one of them (an MC0020C) gets the ROM 7 disabled when you connect the LowerROM, the other (an MC0020I) does not.

Haha, I discussed this with Bryce about 28345697 times - and finally You prove that external expansions can disable the internal ROM 7 !!! Thank's!!! That clearly explains a lot. 

[IanS]

[size=78%]Ouch!, my 6128 not match with the schematics.[/size]
[/size]

[/size][size=78%]Which version does it match? - [/size][/size][size=78%]http://www.cpcwiki.eu/index.php/Mainboard_Versions[/size]

[IanS]

[size=78%]Haha, I discussed this with Bryce about 28345697 times - and finally You prove that external expansions can disable the internal ROM 7 !!! Thank's!!! That clearly explains a lot. [/size]

Yes you can disable the internal DOS rom via the expansion connector on some editions of the 6128, but not all.

[Bryce]

Exactly! That's what I've been trying to tell TFM for a long time.

Bryce.

[gerald]

Haha, I discussed this with Bryce about 28345697 times - and finally You prove that external expansions can disable the internal ROM 7 !!! Thank's!!! That clearly explains a lot. 

Well, he 'proved' that external expansions can disable the internal rom 7 on SOME 6128. And discussing that 28345698 or more will not make this work on ALL 6128  .
Talking about proof, it would be nice to :
   1. identify revision of board that can disable ROM 7 from external extension.
   2. Get an updated schematic for these revision.

[gerald]

Ouch!, my 6128 not match with the schematics.


Pin 13 of IC210 is not connected with R211 in any side, and seems to be not used.

I think the best way in my case is to use the first solution proposed by Bryce. The function of pin 20 in a ROM is known and sure.

Schematic in the service manual is for board revision MC0009A (and should be valid for MC0009 in general).

In the Amendmend service manual, while the floppy section schematic is not available,  from the PCB (MC0023A revision) you can see that the gate that drives pin 13 is not used at all, but also that R211 is now connected to pin 10 of IC210. A quick look seems to indicate that they changed the gate assignment when changing the floppy data separator (ie, there is one 74LS132 gate free now).
So the modification should apply, but on pin 10 of IC210 instead of pin 13.