SVI 738 ULA reverse engineering

By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 00:11

Hi!

In my work with a proper memory mapper for SVI738, understand that the SLT logic is not correct, and does modes for adding 256-4MB dram that Henrik Gilvad introduce do not work as expected to the MSX2/MSX2+ standard.

Even that we can do a conversion with VRAM 128KB and BIOS for MSX2/MSX2+ with replace of the VDP works we still have the issue with the mapper. Even if we successfully have a mapper working we will have that RAM in SLT2 or SLT1, which is not as the MSX2/+ standard apply, we would like to have it on SLT3-2 or SLT3-3.

So in this work, I decide to go for the ULAs and replace does with CPLD, specially the ULA9RA041 but also the ULA5RA087
do get replacement if does are broken Smile, I have study the MSX Data Pack, Expert 2/3 schematics, also some PHILIPS manual, Yamaha and Sony to try to reverse engineer does ULA, and correct the ULA9RA041 logic, to get a correct mapping of SLT3-x and also the FFFF signal.

I think I have made a embryo, but please advice or comment the schematics, also a VHDL project will start, if you are good a VHDL and want help .. please contact me Smile

The new ULA replacement for ULA9RA041 have added logic and will need additional Adrees Ports A2-A5 and A7-A13
and the pin 40 is not used anymore, also the (parts of IC) IC42 and IC29 are not in used, new signal will be connect direct to pin 1 on IC63 also pin46 will be connected direct to /SLT3 signal as input

Idea is to use socket that connect to CPLD (MAX 7000S) for replacement as PIGBACK PCB

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By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 00:14

By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 00:16

ULA5RA087 - reverse engineering prototype schematics Tongue

By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 00:17

ULA9RA041 - reverse engineering prototype schematics Tongue

By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 00:19

the i8255-2 IC VHDL code from OpenCores will be used, so that part is already finished Smile - done by other RetroProject

By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 00:19

the i8255-2 IC VHDL code from OpenCores will be used, so that part is already finished Smile - done by other RetroProject

By Manuel

Ascended (15754)

Manuel's picture

02-10-2019, 09:24

FYI, AFAIK the standard does not prescribe in which slot the memory mapper should be. So, any slot is OK, according to the standard.

By lkpalwa

Expert (92)

lkpalwa's picture

02-10-2019, 11:04

Yes, but most of MSX2/+ use the 3-n as the mapped ram slots, I have heard there is issues to have mapped ram on slot 1/2
does slot are normal for carts and expansion Smile

from the wiki

In MSX2 slot 0 is usually expanded. Same goes with slot 3. This is because these computers need to point more memory because they need Sub-ROM and maybe also disk drive, Kanji ROM, firmware etc. In these computers main BIOS is in slot 0-0 and Sub-ROM in secondary slot 0-X or 3-X.

By Manuel

Ascended (15754)

Manuel's picture

02-10-2019, 11:39

That is due to the used MSX Engines mostly, I think, but there should be no issues to have RAM in slot 1 or 2. Otherwise, indeed, RAM expansion cartridges would not work properly.

By Omega

Master (213)

Omega's picture

11-10-2019, 14:37

This is a very cool project, making a replacement ULA is important for preservation of these machines in the future. ICs do not live forever and custom ICs like ULA are unobtainable today.
Cool

By alexito

Hero (555)

alexito's picture

11-10-2019, 20:29

I agree with Omega. If you put a link for donation for this project I'm glad to contribute with you.