16k cartridge to 64k expansion

Page 4/6
1 | 2 | 3 | | 5 | 6

By zeilemaker54

Master (211)

zeilemaker54's picture

21-10-2017, 13:57

Hmm. I remembered wrong I guess. Yamaha cx5mii has it for sure....

By gdx

Paragon (1651)

gdx's picture

21-10-2017, 15:30

Routine found in MSX1 Bios of Yamaha CX5MII, CX5MII-128 and some YIS-503IIR. Found also in unofficial Bios (v1.3 & v1.4) for the Epcom HB-8000.

By Grauw

Enlighted (6262)

Grauw's picture

21-10-2017, 15:34

CX5MII has memory mapped internal RAM so indeed it does initialise it.

CX5MII was really a bit of an inbetween-MSX1-MSX2 model. Pretty awesome computer.

By marcoexo

Resident (39)

marcoexo's picture

21-10-2017, 23:35

Ok, I finished tracing down the schematic for the 16k expansion. It looks like an easy task to accomodate for the full range. I believe it is sufficient to tie down pin 2 of the 74ls74 excluding the two bit selection logic for A14,A15 as my simulation suggest (I used cedar logic simulator, nice and easy tool)

Look the files here https://1drv.ms/f/s!Amj-hhyUuUxAk6Bjc40pUUqgxrvhVw
(.cdl opens in cedar logic simulator)

As for the refresh logic, AFAIK it should be possible just to connect RAS to MERQ on the bus, but on this card it's implemented a logic based on a counter which toggles 128 times the A7 line, I'm not a Z80 specialist but this should be ok regardless the amount of ram, is it so ? If it's not so I think I could just use the MERQ signal (not actually used bu the card) and bypass any actual logic, what do you suggest ?

Edit: none of the /CS signal is used on the card, pins are not connected on bus...

By marcoexo

Resident (39)

marcoexo's picture

22-10-2017, 00:56

UPDATE : You won't believe it, but I just made this little hack :

Following Grauw intuition on compatible software , I relocated the 16K RAM to page 1, (4000-7FFF) by swapping A15 and A14 connections (to change selection logic from 1-0 (page 2) to 0-1 (page 1) ) And... My 48K Games now work on CX5M MSX1 !
I Tried just with the one that didn't work, but there's no reason for others to fail.. I think

https://1drv.ms/f/s!Amj-hhyUuUxAk6BoH12VC96ba57BkA

By Grauw

Enlighted (6262)

Grauw's picture

22-10-2017, 02:55

Great! Yes, that would be a simple change that would totally work! Smile

By alexito

Master (153)

alexito's picture

22-10-2017, 03:24

Great Hack!

Congratulations!

for a 16KB External RAM Cartridge but would be awesome to install that cartridge inside the computer (CX5M) using one free Slot I think Slot 3-1 or 3-2 is free.

Hannibal

By Alexey

Paragon (1233)

Alexey's picture

22-10-2017, 04:02

Nice! Does the TESTRAM find and successfully test all available 48kb of memory?

By marcoexo

Resident (39)

marcoexo's picture

22-10-2017, 11:25

Thanks, I don't have a disk yet, I think testram relies on dos, is there any other ram test just based on bios ?

By marcoexo

Resident (39)

marcoexo's picture

22-10-2017, 11:35

alexito wrote:

Great Hack!

Congratulations!

for a 16KB External RAM Cartridge but would be awesome to install that cartridge inside the computer (CX5M) using one free Slot I think Slot 3-1 or 3-2 is free.

Hannibal

Yes, someone already did this using an expansion and a subslot 3.x to handle both memory and the already existing FM catridge on CX5M, but that uses a sram, which is also simpler to implement.
http://www.msxpro.com/cx5m.html

Page 4/6
1 | 2 | 3 | | 5 | 6
My MSX profile