Converting a 50Hz to 60Hz MSX1

Ah, The eternal struggle between 50hz and 60hz, PAL vs NTSC, Japanese vs European... but have no fear: Z80ST is here! Only recently presenting the scene with QBIQS, now SapphiRe provides us with an article which demonstrates the hardware buffs how to replace the VDP of 50hz MSX machines with a 60hz specimen, in order to finally boot Japanese ROMs at correct speed. This technique may come in handy for both gamers and developers wishing to test their software in different configurations. The article, including some neat, clear photos, is written in Spanish, but non-speakers will surely make amends using Google Translate.

Relevant link: Z80ST blog

Comments (12)

By selios2000

Champion (321)

31-03-2011, 17:48

My God! I usually did it via basic!

By Google

By snout

Ambassador (13691)

31-03-2011, 18:04

on a MSX1?!

By NYYRIKKI

Prophet (2771)

31-03-2011, 18:51

If I understood correctly this will output PAL 60Hz ? (Instead of NTSC 60Hz that original Japanese computers output)

By Huey

Prophet (2132)

31-03-2011, 20:09

PAL 60Hz. Wouldn't NTSC require an (not present on Toshiba HX-10) RGB connector?

-------------------------------
TMS9918(A)
* colour-code: NTSC
* refresh: 60 Hz.

TMS9928(A)
* colour-code: YPbPr
* refresh: 60 Hz.

TMS9929(A)
* colour-code: YPbPr
* refresh: 50 Hz

By SapphiRe

Master (253)

31-03-2011, 20:29

Must do some more tests, because the flat TV we have on the living room doesn't like the output of the modded HX-10. As soon as I can I will take some pictures of the output on that TV.

By NYYRIKKI

Prophet (2771)

31-03-2011, 22:47

Usually old European monitors/TV's manages to show colors correctly only PAL 50Hz and PAL 60Hz when using composite connector. Naturally this is other way around if you use monitor from USA or Japan (Only NTSC 50Hz and NTSC 60Hz show colors correctly) Usually trying to show NTSC picture on PAL monitor results to B/W picture with stripes.

A bit more modern TV's may have manual setting to select witch color encoding is used. -> Good idea to check out OSD menu options, if available.

Modern LCD TV's and video projectors usually tend to select color encoding automatically and they show colors correctly on PAL 50Hz, PAL 60Hz and NTSC 60Hz, but most of the times NTSC 50Hz signal detection fails and result is B/W picture. Actually I've come across only one a bit older ViewSonic video projector model that managed to show all the 4 combinations that are used by MSX computers without problems.

On latest models it seems that things are going more wrong again... I think that from manufacturers point of view things like FullHD and HDMI are much more interesting than functionality of low resolution analog inputs... One other related problem is that MSX (and other old consoles) typically output progressive picture while LCD TV's / Projectors tend to accept only interlaced picture trough low resolution analog inputs. (With "low resolution analog inputs" I mean non VGA analog inputs.)

By selios2000

Champion (321)

01-04-2011, 10:23

I did it in the MSX1 Yamaha... maybe it worked out due to its "special" VDP.

By SapphiRe

Master (253)

01-04-2011, 12:43

@selios2000 probably your Yamaha has a 9938 inside, instead of the 9929/9928 commonly present on MSX1 machines.

By sd_snatcher

Paladin (842)

05-04-2011, 21:00

Nice work, Z80ST! The TMS9928 is the VDP used on Brazilian MSX machines.

An extra tip: to complete the conversion, you also need to update the BIOS, otherwise the BASIC PLAY command will play the notes at the wrong speed.

Curiously enough, the Sharp Hotbit had this known bug: it's PLAY command was based on 50Hz timings, so any BASIC music played on the original Hotbit will play too fast. There are some ways to fix this though (which are the same for your Toshiba HX-10 with a TMS9928):

1) Change the BIOS for a japanese one, adjusting the keyboard map/decoder, character set and the BIOS IDs 002Bh/002Ch
2) Connect and MSX-Music or MSX-Audio and issue the CALL MUSIC/CALL AUDIO command. Then the PLAY command will work at the correct speed.

By SapphiRe

Master (253)

06-04-2011, 08:40

@sd_snatcher yes, that's the next step, but I guess I will just change the MSB of $2b of the original BIOS, to convert it to a 60hz BIOS on a European machine

By pitpan

Prophet (2560)

07-04-2011, 13:16

But you can emulate that by just:

- Copying ROM page 0 to RAM (0000h-3FFFh -> RAM)
- Select page 0 to point RAM
- Patch ROM copy in RAM
- Dump patched ROM copy to RAM in page 0

Voilà. But keep yourself DI or prepare to reset

By SapphiRe

Master (253)

08-04-2011, 00:22

@pitpan, indeed, but doing that you loss 16kb of RAM, but for a fast test it's the best option. But a hardware patch that need a software patch makes no sense to me. If you replace the VDP chip, it seems more logical to replace the BIOS itself

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