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V9958 Video Board

A project log for MSX COMPATIBLE BOARDS FOR RC2014

Create a series of boards designed for the RC2014 bus to achieve MSX/MSX2 compatiblity

Dean NethertonDean Netherton 11/14/2020 at 02:181 Comment

Created and tested 2 V9958 designs.  One using the Sony CXA1645 chip to generate RGB, Composite and S-Video signals.  Another that only outputs RGBs signal.

The various designs for video boards that i found online, use DRAM memory chips to get 128k or 192k . I didnt want to use those for a few reasons, so I went with a design that uses an SRAM chip - the 512k chip (ASC6C4008).  This is similiar to many of the TMS9918 modern implementations.

The benifits of going with SRAM are:

I wasnt really sure if the timings would all work --- I looked at the datasheets and it all seemed to be in the realm of possibility - The paper by Tom LeMense was very handy in helping me understand some of the things that would need to be consider.

I mapped the 3 CAS lines from the V9958 to the top 3 Address lines of the SRAM, allowing the video to access a full 192k range - the other memory address are simply ignored.  I havnt fully tested all RAM access operations - only been running it in TMS9918 compatibility mode....

A few things to note:

RomWBW works fine with the board, using its TMS driver - the V9958 is backwards compatible to the TMS9918

I had a few design faults with my boards -- manually 'adjusted' the boards - but i will get new ones made soon.

I havn't tested PAL mode, nor tried writing software to utilise the extra features of the V9958 chip - such as its higher resolution.

The designs for the boards 'borrow' from many other projects, in particular the Rosco 68K video board, for understanding how to create a simple RGBs output.  The Omega MSX for a working implementation using the CXA1645P chip.  This guy. And the numerous google searches and various forum postings.

Next steps:

1. Get new boards made that fix minor layout issues - also try and improve signal quality

2. Write some software to use the higher graphics modes.

3. Update RomWBW tms driver to detect v9958 chip and flip to 80 column text.

4. Get an OSSC to test out RGBs video.

References:

https://cdn.hackaday.io/files/5789247676576/9918-SRAM.pdf

https://github.com/rosco-m68k/hardware-projects

https://github.com/Xeraster/z80computer

Discussions

zpekic wrote 04/16/2021 at 06:43 point

Cool project! Here is my attempt playing with V9958 - https://hackaday.io/project/178481-msx2-video-to-vga-conversion-proof-of-concept

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