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Author Topic: External colour input (Read 5922 times)

Offline pear

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Re: External colour input
« Reply #30 on: 2016.December.05. 09:57:02 »
Maybe Col0 is brightness. ZX Spectrum has 8 colors (3 bits Col1-Col3) plus brightness.

Offline lgb

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Re: External colour input
« Reply #31 on: 2016.December.05. 10:26:47 »
The TVC Spectrum emulator schematics are very clear for my poor knowledge. Extc\ is always put to ground, and it seems that Col0 is used for transparency, leaving Col1-Col3 for the colour input.

\EXTC is on ground (low active) since the whole screen wanted to be "driven" externally, not just a part of the screen, as eg. a sprite, or such. I think.

Offline Zozosoft

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Re: External colour input
« Reply #32 on: 2016.December.05. 10:31:17 »
Pear! What do you think: the TVC Spectrum Emulator do anything than emulate the Spectrum screen?
If I see right then it is only modified Spectrum ROM (keyboard reading, sound. Probably tape?) with the emulated screen. Then it is only enought for a BASIC program running.

Offline Zozosoft

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Re: External colour input
« Reply #33 on: 2016.December.05. 10:37:17 »
\EXTC is on ground (low active) since the whole screen wanted to be "driven" externally, not just a part of the screen, as eg. a sprite, or such.
Yes. And it is also possible do on Enterprise.
If my theory right about the EC lines in Hires 2 -> 16 color then possible 640x resolution with 16 colors on external graphics! (736x300 if full borderless)
But for this need some hw acceleration: scroll registers, block operations (copy, fill, etc)...
Plus the sprites :-)

Offline lgb

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Re: External colour input
« Reply #34 on: 2016.December.05. 11:47:40 »
Yes. And it is also possible do on Enterprise.
If my theory right about the EC lines in Hires 2 -> 16 color then possible 640x resolution with 16 colors on external graphics! (736x300 if full borderless)
But for this need some hw acceleration: scroll registers, block operations (copy, fill, etc)...
Plus the sprites :-)

This was my idea too, SymbOS would look great for example :-D Basically it's almost the user experience of GFX9000 etc then :D Though those stuffs are fast enough even using "private to the video chip" VRAM, since there is some hardware acceleration, what you say above exactly, Zozo. It would be rather interesting (though a complex project, I guess it would need an FPGA already ...) to implement something like the video chip used by MSX2 or even better the V9990 (or what is that which is used in GFX9000?). The extra value of this, if it's implemented in a way, that the "main screen" of the emulated entity can be even turned off, and just its sprites remains:

* there can be a Nick + sprites like configuration, by switching the "main external screen" off, but not the sprites
* maybe even MSX emulation (!) on EP at some level at least, since then the external gfx unit can be MSX/MSX2 compatible, or whatever
* you can even mix Nick/external gfx if the latter can use the /EXTC line from memory too
* other tricky mixes, by using the two bits on port 0x80 which controls the process
* to simply get a nice, high resolution screen as whole, ie that 736x300 16 colour and similar

Then it's kinda multi-purpose stuff, however this is far more than a "little logic" ... Unfortunately - I think - a real V9958 or such cannot be used, as it hasn't got digital (?) outputs to feed on external colour inputs of EP, and even if it has, maybe it's not possible to "sync" on the video clock (and custom vsync, dictated by vsync mode LPBs etc) of Nick ...

Surely, there are limits, like the 16 colour, a V9958 and V9990 would know more than "only" 16 colours, but that's another question.

Offline pear

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Re: External colour input
« Reply #35 on: 2016.December.05. 12:49:02 »
Pear! What do you think: the TVC Spectrum Emulator do anything than emulate the Spectrum screen?
If I see right then it is only modified Spectrum ROM (keyboard reading, sound. Probably tape?) with the emulated screen. Then it is only enought for a BASIC program running.
It's possible. I have not watch in detail yet.

Online gflorez

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Re: External colour input
« Reply #36 on: 2016.December.05. 14:06:24 »
« Last Edit: 2016.December.05. 20:55:05 by gflorez »

Online gflorez

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Re: External colour input
« Reply #37 on: 2016.December.06. 00:12:50 »
Where the Enterprise designers thinking on CGA or EGA when they created the expansion port colour inputs?

There are similarities: CGA  and Enterprise inputs have a colour deep of 4 bits, with digital signals. But IBM's CGA works on fixed RGB colours while the Enterprise has a palette, like EGA, that has 6 bit of colour deep, with digital signals.

Also the lower graphics resolution of the IBM modes work on near 15Khz horizontal frequency like the Enterprise. But IBM has 60Hz(NTSC) and the Enterprise 50Hz(PAL) of vertical frequency.

On the other side, IBM modes are planar, made of a mix of one layer per colour(+ intensity), while on the Enterprise the colour is on only one layer.

CGA was introduced on  1981, while EGA was released on 1984

Offline lgb

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Re: External colour input
« Reply #38 on: 2016.December.06. 02:33:24 »
Where the Enterprise designers thinking on CGA or EGA when they created the expansion port colour inputs?

I'm not sure I get your point. On EP, these are inputs, they're not suitable to connect a monitor where they're also input. Oh, or you think that using EP "as a monitor", by another computer, so its CGA/etc signal is fed on the EP? It wouldn't work I guess for a simple reason. Not the external stuff (which is connected to the EP) "dictates" the pixel clock, and SYNC pulses ... It's the task of the Nick, and the device connected to the EP's colour inputs should "accept this rule". So it's not the very same issue.

Online gflorez

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Re: External colour input
« Reply #39 on: 2016.December.06. 09:01:21 »
I mean about signals.  There was a time when the computer video information was managed digitally. Then things changed and all gone analogic, Composite video, SVHS, RGB, VGA.

Now, with LCD panels generalised, we return again to digital signals with HDMI.

The Spectrum emulator of the TVC is a good example on how to interface directly that strange colour inputs.

But they wrote about to inject a video image to the Enterprise. What digital standard of year 1984 the Enterprise creators mean? Or was it their own new method with some sort of synchronising interface?
« Last Edit: 2016.December.06. 09:04:56 by gflorez »

Online gflorez

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Re: External colour input
« Reply #40 on: 2016.December.06. 09:12:09 »
Also, I have been looking for a Enterprise contemporaneous graphics chip that outputs some sort of digital signals, but all are analogic.

Is for that I have been reading about CGA and EGA  chip sets.

Online gflorez

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Re: External colour input
« Reply #41 on: 2016.December.08. 08:47:44 »
The MSX chips, TMS9918, V9938, and V9958, all only output analog RGB.

But the Yamaha V9990, used on Sunrise GFX9000 and Tecnobytes V9990 Powergraph(supported by Prodatron in his SymbOS), have a digital output of its internal Color Bus.

See mode 4B\D, I think that it fits the Enterprise if synchronised.




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Re: External colour input
« Reply #42 on: 2016.December.08. 11:10:37 »
On the MSX graphics cartridge the memory can't be acessed directly, but on an Enterprise approach that memory could be paginated just like is done for Nick.

For the higer modes, an external RGB connector can be provided, like on the MSX cartridges..

Offline lgb

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Re: External colour input
« Reply #43 on: 2016.December.08. 17:56:01 »
On the MSX graphics cartridge the memory can't be acessed directly, but on an Enterprise approach that memory could be paginated just like is done for Nick.

For the higer modes, an external RGB connector can be provided, like on the MSX cartridges..

That wouldn't be a problem. As on MSX, video RAM can be local to the video chip and used through the I/O ports. Using a shared memory, ie what is can be accessed via the CPU too is tricky, specially for a system which is not designed for that (like these V* chips). I wouldn't do that. Maybe it's possible via dual-port memory, or some other complicated way, but why would do that, if it's not done by their "main usagers" eithers, ie the MSX computers? :) So it even helps things to be easy, just some I/O ports are needed on the EP, and that's all.

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Re: External colour input
« Reply #44 on: 2016.December.08. 18:40:26 »
It was said long time ago. MSX has a bottle neck with the graphic solutions on cartridge, because graphics have to be loaded indirectly. On Eps whe can paginate the added memory.