I have this CX5M computer, it's really sweet and qute, but it can't run MSX-DOS, and it's a pity.

Did anyone tried to upgrade the memory to 64K? If yes, how did you do that?

I did have some Pioneer 32k RAM packs for sale, but they have all gone, I am sure that the addition of one of them would enable you to run MSX-DOS. Will MSX-DOS work with RAM in different pages though ?

Pigback more memory in the cx5m and use a '138 to select the chips on the higher adress. Or take all the memory chips out and use an old 64K x 8 chip from a 486 motherboard (cache) connected to the bus

What are you saying? I have two options

A) Piggyback extra 4116 chips on top of existing 8 chips (I think that's what's inside), except for /CAS signal? And then piggiback 74F138 chips (1-of-8 decoder/demultiplexer) on top of some other 74Fxxx chip for power (pins 8 and 16) and have the rest of pins straightened and hang in the air? Now I guess I need to hook some pins of 74F138 to some address lines, and some other pin to /CAS pins of second row of 4116 chips? Then how exactly shoud I connect it?

B) Use some crazy SRAM chips? What about refresh signal? Can you replace DRAM with SRAM without any glitches?

Ups, CX5M uses two 4416 (16Kwords of 4-bits) chips for main ram.

Also, it looks like RAM is located in the upper half of SLOT 0, right above 32K of BIOS and BASIC roms...

So before adding extra 32K ram, I think I have to move existing 32K RAM to SLOT 3... How do I do that?

Ok, in CX5M, slot 3 is completely used by SFG-01 unit. That means I can't use SLOT3 for memory, and keep SFG as well, because there is no mapper inside, like on CX5M-II/128. Very interesting...

Looks like here is some sort of instruction on how to get 64K RAM in CX5M using two 61256 SRAM chips:

https://listas.unesp.br/pipermail/msxbr-l/2004-October/023631.html

If anyone can make a good translation from Portugese, it'll be awesome!

(note by Alexandre_Taito: I edited the link!)

So here we go, the full e-mail translation. Original by Luciano Sturaro (http://www.msxpro.com)
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More curiosities,

The CX-5MU doesn't have a RF modulator, only composite video, beyond the fact it is 120V / 60 Hz (it is on the sticker)

If I'm not mistaken, it is NTSC, I gotta see the crystal frequency to be sure

The inverse slot I solved in a pratical way but a little "ham fisted": Got an edge connector, closed the pins in a way they were flush to the board, and soldered (yes, soldered!) it in the board. It is very sturdy and you can even put a mini slot expander from ademir there.

I've heard thru the grapevine this slot is to plug "exclusive" peripherals from yamaha, and one of that is the drive interface, that already has the other 32K missing for it to work. I've never seen one of that

This CX5-MU was bought in a surplus shop at Santa Ifigenia (Note from Translator: a kind of "akinabara" of Sao Paulo, Brazil), bought it working, with the sound cartridge and the musical keyboard

Since it didn't recognized the drive interfaces, I expanded its' ram, but at this time I didn't had the schematics, and fried the MMC (n of t: Memory Management Chip) chip (YM5214) and the puter stayed here getting dirt for some good pair of years. I almost canibalized it and modified the sound cartridge to be used on the brazilian Expert, but it would be a shame

Someday I had the idea of putting my SRAM cart on that (n of t: link for the SRAM cart schematic: http://www.msxpro.com/sram64k.html but please visit http://www.msxpro.com ) to see what happens and the puter worked! So I found its schematic and found that only the /CAS and /RAS lines of the MMC were fried. The rest was good. Since this moment I understood that I couldn't expand it's original RAM easily, because the slot assignment is very strange:

Slot 0, page 0 - ROM
Slot 0, page 1 - ROM
Slot 0, page 2 - RAM 16K
Slot 0, page 2 - RAM 16K

Slot 1 - upper connector
Slot 2 - back connector
Slot 3 - sound expansion

So, where would I put this 32K of ram or new 64K? Worse, I'd have to make new /CAS and /RAS signals for the DRAMs since I fried them in the MMC (MMC means MSX memory controller, it is on the service manual)

Pratical solution that works:

Build a 64K memory bank with a pair of 61256 (SRAM) (NofT: You can get an old 486 motherboard and get a pair of 61256(32K) OR just one 61512(64K) chips from that. These are very common cache memory chips on old 486 motherboards). Just that solves the problem of Refresh. Just used the idea of the SRAM cart I've built some time before

I did that inside the puter, the two SRAMs I put one in top of the other, minus the /CE of each one, piggbacked in top of the ROM chip. The 74LS04 and 74LS02 in the top of VDP. Connected everything on the Slot 2 and BINGO! It worked, even with a drive interface.
O segundo passo era não perder esse slot e ficar com um unico slot
livre. Solução, expandir um slot.

I've built a very simple slot expander, no buffering, in a universal veroboard (and some wire-up), a nest of cats but it worked.

Best option I found:

Slot 3 to the RAM

Expand the slot 1

Sound expansion on slot 1.3
Upper connector on slot 1.0

No slot expansion on the back slot, because if you want to connect a slot expander, there is possible.

If someone wants to make a CX-5 work with drives, this is one solution. Take the original RAM chips out and that's done!


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Thanks a lot for your help!

I like the idea of external 64K SRAM cartridge. I don't need the battery backup and write protection seatures, so it's going to be very simple for me. D0-D7 for data, A0-A14 for 32K of addressing each 61256 chip, chips A and B are enabled using two AND and one NOT elements:

Chip A enabled, if "SLTSL AND NOT A15" i.e. SLTSL=1 and A15=0
Chip B enabled, if "SLTSL AND A15", i.e. SLTSL=1 and A15=1

What are all those 56K resistors for? Is it a part of leaking power on disconnection? I don't think they are necessary.

Now, how would I expand SLOT0 and make music cartridge connectors SLTSL signal go high only if SLOT0-1 selected?

I also need to move BIOS and BASIC rom from SLOT0 to SLOT0-0? Should I cut the /CE singnal from ROM chips with bios and basic from SLOT0 SLTSL, and make some sort of circuit with will set /CE to high only if SLOT0 and subslot 1 selected?

Uhm, very tough stuff

Dhau, I'll do a little schematic here and upload as soon as possible. I don't have a identical machine to reproduce with photos (any brazilian with a spare CX5M to donate? he he he) but I'll do my best to create a simpler "cut here, solder there" tutorial and put online.

Thanks, it's a great idea.

wow.

I have a Philips 64k user RAM Expansion cartridge (VU0034), if it it would serve your purpose I'm willing to trade.

That's what I've been curious about (I'm a complete computer amateur). As the CX5M has the back cartridge slot, if this back slot was filled with a RAM expansion cartridge, would the computer now be as if it was 64k?

hey unicorn, you still have the 64k ram cart?