256KB expanded memory trouble (NMS 8280)

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By Kamelion

Supporter (15)

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05-02-2014, 11:59

Hi All !
I’ve had expanded my NMS8280 to 256 KB of ram , following the instruction provided here http://msx.hansotten.com/uploads/msxdocs/nms256kmemory.pdf

Drawing these instructions onto schematics , we got this modification.

The computer seems to work properly, but if I perform the test of the ram with the software TestRam , I get the following results :
- Base ram = slot 3.2 , 64 KB (test result OK)
- Memory mapper = slot 3.2 , 192 KB (test result OK)

So, 64KB of ram are missing. Considering that I’m new regarding the MSX system , I’m not able to understand where is the problem . Of course I checked all components , the soldering and wires , but all seems ok.

Have you any clues, any ideas ? Is possible to do more tests , perhaps in Basic ?

Many thanks in advance.

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By Kamelion

Supporter (15)

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05-02-2014, 12:01

Sorry for double post !

By msd

Paragon (1477)

msd's picture

05-02-2014, 12:11

- Base ram = slot 3.2 , 64 KB (test result OK)
- Memory mapper = slot 3.2 , 192 KB (test result OK)
Together this is 256KB ram.. Use another test program to check it. All memory is in the memory mapper.. Spiting it into base ram and memory mapper is a little misleading.

By Daemos

Paragon (2009)

Daemos's picture

05-02-2014, 12:14

Looks good. 64 + 192 = 256.

I guess the program means by base ram the RAM it finds and checks at start and then continues cycling through the mapper to find out whats more to find.

By Kamelion

Supporter (15)

Kamelion's picture

05-02-2014, 12:26

Thanks.
Uhm... I'm quite sure that the value in "memory mapper" entry , should be the total amount of ram (256 KB and not 192), also because if I check on emulator bluemsx, for a 8280 with 256KB , the TestRam software shows base ram entry=64 and memory mapper entry=256.
BTW, the software CHKMEM.BIN reports a total of 12 pages on slot 3.2 ; 12pages X 16KB each page = 192 KB ....

By Jipe

Paragon (1559)

Jipe's picture

05-02-2014, 12:37

can you post a biggest schematic

By flyguille

Prophet (3028)

flyguille's picture

05-02-2014, 12:40

splitting RAM in differents slots is quite unusable very few MSX software if NONE will be smart enough to use both RAM.

and the MSX BIOS don't uses the slot with bigger RAM as main ram, it uses the first found from slotting numerical count up point of view.

MSX bios also don't shows the sum of several RAMs mapped (on the bootup message).

Except for very custom software is useless.

By Jipe

Paragon (1559)

Jipe's picture

05-02-2014, 13:00

i have a same schematic but is added a 74ls08 between the 74LS139 out put and the /cas of memory
send me an e-mail please

By Kamelion

Supporter (15)

Kamelion's picture

05-02-2014, 13:08

@ Jipe : I can't now , sorry. What is not clear on schematics, may be I can tell you
@ flyguille : if I'm not in error , this mod use the same slot (3.2 , the default slot for the 8280) both for base ram and the added ram... but I could be wrong... If you can explain me why you say that the ram is splitted in different slots , is very appreciated Big smile

By Kamelion

Supporter (15)

Kamelion's picture

05-02-2014, 13:16

@ Jipe : you've a mail Big smile
74LS08 ? it's an And gate... in "AND" with which signal ? Have you the schematic ?

By msd

Paragon (1477)

msd's picture

05-02-2014, 13:33

@flyguille: For dos2 this is completly different.. It will take the biggest ,can use several mappers does count all the memory. So this is not very custom software..

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