Is there any software built for V9990 for 50 Hz and interlaced modes?

Paragon (1232)

11-02-2023, 20:36

I read LCD flickers at 50 Hz. Interlaced modes are not supported, progressive scan modes only.
Is there any sense making software for these modes?
Or, slightly different, but related question - is support for 50 Hz mode and interlaced scan vital and required?

Another not related question: datasheet says 25.2 MHz master clock for mode B6, but there's no such clock fed into the chip, only 14.3 MHz and 21.5 MHz. How is it possible?

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Por bore

Master (182)

11-02-2023, 21:13

Eugeny_Brychkov wrote:

I read LCD flickers at 50 Hz. Interlaced modes are not supported, progressive scan modes only.

That is entirely up to whatever converts the video signal to something that drives the LCD.

Typically an LCD wouldn't flicker at those frequencies because the capacitance of each cell can hold the value for much longer, but interlace is a bit of a compromise between resolution and framerate.
So depending on if the converter thinks the second frame represents time or position more you'll either get flickering or you'll get those "every other line" traces but that is "conscious" choice of the LCD driver.

If you have an LCD TV that is less than ten years old it might have more advanced algorithm for sorting that out and you'll get flicker free high resolution when the image is still and some merged version when the image changes.

If you use interlace and synchronize the scrolling with odd/even frames you'll get some nice soft flicker-free subpixel scrolling.

Por Eugeny_Brychkov

Paragon (1232)

11-02-2023, 22:16

bore wrote:

Typically an LCD wouldn't flicker at those frequencies because the capacitance of each cell can hold the value for much longer

My research shows that it does not hold true anymore.

bore wrote:

If you have an LCD TV that is less than ten years old

If I have got the problem properly it is relatively hard to find monitors supporting 15 kHz HS. Thus V9990 needs some additional controller, or be used with CVBS/composite or S-video.

bore wrote:

but interlace is a bit of a compromise between resolution and framerate.

Is the frame rate still a problem these days? I think V9990 can display 640*480 non-interlaced?

bore wrote:

If you use interlace and synchronize the scrolling with odd/even frames you'll get some nice soft flicker-free subpixel scrolling.

Vertical scrolling of course? How do you see converting it to the progressive scan?
Or even better: how to achieve this functionality without using interlace nature of scan as is?

Por Eugeny_Brychkov

Paragon (1232)

11-02-2023, 23:27

I think I am starting to get it more or less.

The puzzling question is 640x480 @ 25.2 MHz dot clock without having such a frequency.

By decreasing space of left, right, top and bottom borders (to still fit into horizontal 1365 clock cycles and 525 lines specification)? But it will NOT then be 25.2 MHz, it will still be 21.5 MHz. And it is not possible because horizontal sync becomes too short (max 85 clock cycles < 4 us).