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Technical-Chap

MC-10 PAL memory upgrade, help required

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Hi everyone,

 

I have been playing with a new purchase of an Tandy MC-10 PAL, I have the machine working and the 16K RAM pack, but wanted to get the VDG working with the higher resolutions modes, this requires you adding more memory internally. As I could not find anything on the web about doing this to the PAL version, I took the NTSC and and copied that. Now the only thing I can't find is were you need to change the VA12 line to line VA13 to allow the BASIC to see the extra 4K I have added. You will recall the Tandy had to make a mod to stop the BASIC from seeing more memory then was fitted, as it did not decode the address lines fully. But it looks as if on the PAL versions the MOD has been added to the motherboard. I have not been able to find a schematic for the PAL version or been able to trace were it might be on the motherboard. Any help would be gratefully accepted.

Pictures of before and after MOD:

 

Motherboard PAL.jpg

 

After MOD 01.jpg

 

After MOD 02.jpg

 

After MOD 03.jpg

Edited by Technical-Chap

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On 2/14/2021 at 2:23 AM, Technical-Chap said:

Hi everyone,

 

I have been playing with a new purchase of an Tandy MC-10 PAL, I have the machine working and the 16K RAM pack, but wanted to get the VDG working with the higher resolutions modes, this requires you adding more memory internally. As I could not find anything on the web about doing this to the PAL version, I took the NTSC and and copied that. Now the only thing I can't find is were you need to change the VA12 line to line VA13 to allow the BASIC to see the extra 4K I have added. You will recall the Tandy had to make a mod to stop the BASIC from seeing more memory then was fitted, as it did not decode the address lines fully. But it looks as if on the PAL versions the MOD has been added to the motherboard. I have not been able to find a schematic for the PAL version or been able to trace were it might be on the motherboard. Any help would be gratefully accepted.

Pictures of before and after MOD:

...

Just be aware the original published mod for NTSC machines had a bug.  Some changes were published, and I think they are on Discord, maybe in a facebook group as well. 
 

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Yes, I had read this: https://thezippsterzone.com/wp-content/uploads/2020/06/8K-mod-article.pdf and his article about the mod required for the 4 chip version and then by looking at the picture's I was able to see his own 2 chip upgrade and add it to the PAL MC-10, https://thezippsterzone.com/2020/06/12/mc-10-8k-internal-mod/. My issue is that it is not seen by the OS, it works really, I can poke at address's into the memory above 4K, but the BASIC will not see it, in his own article he says you need to change the A12 line address decode to A13, But without the schematics for the PAL MC-10 I can't work it out.

 

Does anyone know were I could get hold of a copy of the schematics for the PAL version?

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Will this internal ram mod conflict with the external ram ? I have seen a problem with this somewhere..

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Hi Mr Dave, I have tested mine with the RAM pack installed, it will only show the 19,xxx old free, but loads and plays games just fine, no screen corruption or system hangs. I did read the 4 chip solution in the PDF file above does give this problem, but the chap that wrote the 2 chip solution has a fix for that too.

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The factory ROM should just write/read memory looking for the end of RAM and then set the top of RAM according to what it finds.

 

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So after reading about the way Microsoft tested for memory and the fact Tandy did not decode the address lines fully on and NTSC unmodified motherboards, the 4K of RAM is ghosted in the two 4K blocks that make up the 8K block from H4000 to H5000, this would mean BASIC would see 8K when only 4K was real, to get around this Tandy added a hardware fix to check when the BASIC had gotten to H4799 and tell BASIC it had ran out of memory. Now if you do the mod in the PDF above so you can have the higher video modes, you need to change the address to allow BASIC to see the full 8K of RAM and the easiest way is to move the address line up one place (A12 to A13), as the chap says in the document, this on the NTSC motherboards is shown, but as I have a PAL motherboard and the PAL system has the address fix combined on the motherboard some how, I don't know how to make the hardware change for it to work for the PAL motherboards. If anyone has the PAL schematic I could work it out.    

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Justa shot in the dark; but can be the Matra Alice 4K, the french PAL MC-10, a perfect clone including schematics?, if so, there's a lot of info here: Alice en détail

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