Superimposer

By protek

Expert (123)

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14-07-2010, 09:42

Are there any 3rd party or homebrew superimposers available for the MSX2? I read about this feature in an old Mikrobitti magazine, where they reviewed the Sony HB G900 and actually tried it in BlueMSX.

From what I understood, you need at least video in and an updated ROM, containing the set video command in order to get this feature.

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By mohai

Paladin (999)

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14-07-2010, 19:56

For superimposing functions and control, you need to access VDP chip video-in pin so, inernal modification of MSX2 is needed. It is feasable. Sure! But not easy.

I do not know of any home-made superimposer, by the way.

MSX2 BIOS already has superimposing and digitizing functions build-in. No need for extra ROM. If computer can superimpose, then commands will work, if not, they won't.

G900 already has a superimposer built-in, but it needs an external gen-locker in order to activate digitizing capabilities (IIRC).

By protek

Expert (123)

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15-07-2010, 11:33

I had a look at the Philips NMS-8280 service manual. It seems that the superimposition circuitry is located on a daughterboard.

Have I understood correctly: The V7040 chip, responsible of the superimposing, processes the incoming video signal and sends it forward to VDP, which then sends the "complete" signal back to a PAL decoder chip and then to display.

By mohai

Paladin (999)

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15-07-2010, 15:00

I do not have 8280 service manual with me now. Maybe that chip pre-processes video-in signal and then sends it to VDP chip.
VDP chip does all the mixing/superimposing work, then.

By RetroTechie

Paragon (1563)

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15-07-2010, 18:08

G900 already has a superimposer built-in, but it needs an external gen-locker in order to activate digitizing capabilities (IIRC).
Genlock = synchronization of VDP with external video. You need that to superimpose, so HB-G900 also has that. But indeed for digitizing it needs an external unit (same size as G900 case!).

For superimposing functions and control, you need to access VDP chip video-in pin (..)
Only MSX1 videochip (TMS9918A variant) has that. Composite video, but I haven't got a clue how that could be used. Probably needs external genlock circuitry to use it, I doubt there's any MSX1 that includes such circuitry (not something you can add externally to an MSX). Perhaps old/cheap TV studio equipment would use TMS9918A for that purpose. Question

MSX2 VDP doesn't have any video input. External circuitry does genlocking (by varying VDP clock frequency slightly until VDP sync lines up with external sync), VDP outputs a signal that says "background" (color code 0, I suppose), that external circuitry uses to switch between VDP and external video signal. Or perhaps that could even be sent to SCART-equipped TV, with the TV switching between external comp. video & MSX's RGB signals (using fast blanking pin).

With a digitizer, external circuitry digitizes the external video, and sends the data to VDP's color bus. VDP then writes it to VRAM.

By Manuel

Ascended (19270)

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15-07-2010, 19:09

And then we also have the Sony HBI-V1...

and the Victor HC-95, National FS-5500 series and probably some other machines that could digitize.

But for only superimpose there are even more: Daewoo CPC-400S X-II, JVC/Victor HC-7, JVC/Victor HC-30, National CF-2601, Philips VG 8240, Pioneer PX-7, Sanyo MPC-11, Sony HB-701 and probably more.

By protek

Expert (123)

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27-07-2010, 08:34

Regarding this issue, how do the Philips NMS-8250 and NMS-8280, which has superimposer, differ hardwarewise? Do both have the same motherboard and it's just the analog unit that's different?

By Repair-Bas

Paragon (1165)

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27-07-2010, 09:41

The motherboard is the same PCB for the 8250 and 8280
But there are more parts on the 8280 PCB.
and the Video-board is different.
Extra is the front PCB.