Quote:
Originally Posted by dooklink
Can you link me to any evidence for the signal strength issue? I believe I know what the problem is, but I haven't measured the voltage levels yet.
Usually the chip has dynamic range expansion enabled. This way over saturates the Luma, ie brightness. The chip does all of it processing in YUV and converts back to RGB for that output type.
My settings should have the output DRE turned off, but there are other things that still need optimising. I'm just trying to determine if the problem is circuitry, ADC/DAC or Digital Processing settings.
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The first problem is with the use of an LM1881/sync strike type device. Continued use will eventually destroy the GBS-8220, it'll take 18 months to two years though. The LM1881 outputs 5V CMOS levels. The GBS-8220 accepts 3.3V LVTTL levels, when you exceed the device power supply (3.3V) with an input signal, you start damaging the microchip.
Reducing the Amiga Composite sync (5V CMOS amplitude) from 4.8V to <1V cured over 95% of problems with SCART TVs. A SCART TV expects a 1V signal.
The GBS-8220 (TVIA-5725) expects a TTL signal, logic 1 is >2.0V but less than 3.6V max, logic 0 is <0.8V and no less than -0.3V.
The black level offsets are important, from there all scaling takes place. I have not seen a gain control register yet but some chips can amplify or attenuate the incoming video to maintain a 100 IRE level. If it does not, we may need to play with external components or settings. I need play time
Have you played with the decimation filters?
The RGB YUV block can affect the output video if the wrong polynomials are used. Are there any particular colours that look incorrect?
With most video issues, I need to see the issue, on a calibrated monitor, to comment. Photographing a monitor is not easy.
Sorry if some of my answers are a bit vague, I'm still studying the TVIA-5725 chip.