Hi all,

as i've said while ago, i tried to load some YRM-ROMs in my CX5M, which didn't succeed because the CX5M has a bit strange Memory Organisation ($0000.$7fff BASIC, $8000.$FFFF RAM). Usually the YRM-ROMs seems to be located in the full Basic-Area when inserted. So i thought, "piggipack" a 50256-SRAM onto the BASIC-Mask-ROM could do the Trick, since its adress lines and Data lines are the same, which are used on the Slot-Connector (the 50256 has a nearly similar pinout to the ROM). So i've connected A0-A14, D0-D7 to the ROM, WR/RD (CS) to the CPU, OE to the SLOT1 of the MMU, added VCC and GND, connected Pin44/46 on the Slot. Then 've tried to load a .wav-converted ROM; but i have no idea, if this was sucessfull or not (usually it does). Anyway, now the ROM-File should be loaded onto the 50256-RAM. Ok, made a Soft-reset by pulling Pin26 on the Z80 to GND, and nothing happens; it boots normal up instead of searching for the "ROM" on the 50256.

Any suggestions what i'm proably doing wrong?

Many greetings
Stef

Quote:

i tried to load some YRM-ROMs in my CX5M, which didn't succeed because the CX5M has a bit strange Memory Organisation ($0000.$7fff BASIC, $8000.$FFFF RAM).

Which is the normal memory layout for an MSX machine with 32K of RAM...

Quote:

So i've connected A0-A14, D0-D7 to the ROM, WR/RD (CS) to the CPU, OE to the SLOT1 of the MMU, added VCC and GND, connected Pin44/46 on the Slot.

I'm no hardware expert, but I'm having doubts whether hooking up /WR and /RD to /CS is correct (or is that not what you meant with "WR/RD (CS)"?) And I'm missing a connection for /MERQ.

just 2 cts...

Quote:

Quote: i tried to load some YRM-ROMs in my CX5M, which didn't succeed because the CX5M has a bit strange Memory Organisation ($0000.$7fff BASIC, $8000.$FFFF RAM). Which is the normal memory layout for an MSX machine with 32K of RAM... Really? I always thought that on other MSX-Machines is the memory organisation different. Quote: So i've connected A0-A14, D0-D7 to the ROM, WR/RD (CS) to the CPU, OE to the SLOT1 of the MMU, added VCC and GND, connected Pin44/46 on the Slot. I'm no hardware expert, but I'm having doubts whether hooking up /WR and /RD to /CS is correct (or is that not what you meant with "WR/RD (CS)"?) And I'm missing a connection for /MERQ. just 2 cts...

No, this doesn't seem to be the problem (/RD and /WR are of course not interconnected) My first attempt was to write in a memory location which is used by the BASIC-ROM (which doesn't work, of course), but my idea was that the 50256 plays a "mirror" to the ROM-Chip and all write attempts to the ROM would end up in the 50256, so that after a Soft-Reset the contents of the written RAM are available to the CPU, instead of the Basic-ROM. /MERQ must not be used since the Slot-Select-Signal (on the CX5M-MMU=SLOT1/2/3) contains MERQ. For now it seems that the CX5M has found the RAM, but uses it for its own (deactivated internal memory and uses the 50256 as memory instead of the internal 32K).

Greetings
Stef

As ana easy solution, this is waht you can do:

SLOTSELECT - CS
RD - RD (OE)
WR - WR (WE)

Use whatever slot select free signal from the MMU, so RAM chip will be sellected only for that slot, but keep in mind that chip will always be selected even when a cartridge is inserted in THAT slot...
Another bug from this connection is that memory space is mirrored, that is, lower 32k will be the same than 32 high address, but this can be avoided if you do an "OR" with A15 (If A15 and SLTSLCT are 0, then CS=0).
This way you should have extra 32K in the 0000-7FFF address space.