OSSC and YPbPr from TMA9919/29 VDP

Par Pencioner

Scribe (1194)

Portrait de Pencioner

07-06-2020, 23:33

Very curious, as i recently discovered about TMS VDP that it has component output (though computers had CVBS outputs), and now i wonder if MSX1 could be modified to take the component YPbPr signal and feed it into OSSC or RetroTink somehow to get better video image quality? Maybe signals from VDP should be amplified? Just curious, because i was always frustrated with MSX1 video, and at some time my brother would finish soldering OSSC (i ordered DIY kits a while ago but it is on hold now). If wish this would be possible Smile

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Par Louthrax

Prophet (2291)

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07-06-2020, 23:55

Interested too if anybody tries... I’m super happy with my OSSC so far, feeding it directly with the VDP output sounds really nice! OSSC has lots of options like, so maybe no hardware modification would be required ? (And the firmware is open source too)

Par Pencioner

Scribe (1194)

Portrait de Pencioner

08-06-2020, 01:56

At least you have to solder some wires to VDP pins, this is easy enough even for my undecent soldering skills. But, i wouldn't like to try it before someone who is enough skilled with VDP HW to say signal levels shouldn't be amplified, or even (what is more important) - if i have to add some resistance to limit the current to not overheat and burn out the VDP (sic!)

EDIT: ok, quick look to the found datasheet - and there's information that:
"The internal output buffer devices on these pins are source-follower MOS transistors that require an external pull-down resistor to Vss ... ... A 330 Ohm resistor is recommended"

If it is enough to feed then it to the OSSC, that should be simple enough for me to try. If i only were sure i don't have to add some opamps on top of that Smile

Par sdsnatcher73

Paragon (1196)

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08-06-2020, 05:05

Unfortunately these VDP’s predate component video connections and were not designed to be connected directly to a component input. The issue is explained well here. Luckily this guy designed a simple board that will eliminate that issue and will output correctly both YPbPr signals as well as RGB!