1024kb memory upgrade for Yamaha MSX2 YIS503

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By Alexey

Guardian (2464)

Alexey's picture

04-06-2015, 01:14

You have 8 empty places on the board near VDP for VRAM chips. I would attempt to install sockets there and put eight 4164 RAM chips in them. That should make it 128kb of VRAM. In theory...

Alexey

By Grauw

Ascended (8516)

Grauw's picture

04-06-2015, 02:11

A board would be nicer though, then I can keep the CX5MII in its original state. The main board seems so expandable with these add-on boards. I think all the necessary signals are available on the header connector too. Though, I guess without MSX2 BIOS, it’s not so useful to have more than 16K VRAM. Too bad the extra “sub”-ROM with 80 columns support is in slot 3-0 and not slot 0-1 Smile.

I was looking into whether this board would also work with other Yamaha models… The CX7 is probably a safe bet that it does, too. The YIS503IIR doesn’t have a mapper circuit according to its service manual so that one’s probably out (a pic of the board / schematic could confirm if the I/O /MAPWR decoding is there). I wonder about the (Al Alamiah) AX-200 and AX-350, if anyone has any pics of the board or a service manual…

By o.geerdink

Hero (543)

o.geerdink's picture

04-06-2015, 07:56

Alexy if you have it ill take it for my cx5m/ii 128.

By Alexey

Guardian (2464)

Alexey's picture

04-06-2015, 12:52

Ok, the last board reserved for you. Please send me e-mail as a reminder. When the chips come from China, I will assemble the board and then let you know.

Alexey

By l_oliveira

Hero (529)

l_oliveira's picture

05-06-2015, 03:11

8x4164 = 64KB (each chip has 64 kilobits so if you use eight you have 64 kilobytes).

That's a very common memory configuration on MSX1 computers for the mainram.

By Alexey

Guardian (2464)

Alexey's picture

05-06-2015, 09:35

I always mix those bits! Well, then 4x 4464 chips should do the job. In theory. Wink

Alexey

By Jipe

Paragon (1366)

Jipe's picture

05-06-2015, 10:52

in CX5MII you have empty 64k on board 8x4164 and a additional board with 16k
you can modify this additional board with 2x4464
final you have 64k on board and 64k on additional board -> 128K VRAM

By Alexey

Guardian (2464)

Alexey's picture

05-06-2015, 11:57

Probably easier to make a new external board with 4x 4464. But I have no skills to design such board on my own. If there's a demand, this may be done. The original board doesn't look too complicated and 4464 do not need +12 and -5v...

By sd_snatcher

Prophet (3093)

sd_snatcher's picture

18-06-2015, 01:49

Quote:

Too bad the extra “sub”-ROM with 80 columns support is in slot 3-0 and not slot 0-1 Smile.

I don't get it... Why is it a problem?

By Grauw

Ascended (8516)

Grauw's picture

18-06-2015, 10:57

Well, assuming the subrom has to be in slot 0-1... maybe it’s not a requirement. Also that ROM is in page 4000H afaik, I wonder if it’s also mapped to 0000H. My thought was, maybe the ROMs could be replaced with MSX2 ROMs without any hardware modification.

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