eslapion wrote:This spike occur only with colors having a luma level of less than 450mV, that's red, blue and purple
Yeah, I can see how it would not be noticeable above 450mV, since it would presumably be seen simply as part of the rising edge of the higher value.
eslapion wrote:but not with black and only at the beginning of the left border.
This is interesting.
eslapion wrote:However, you can also see there is a downward spike at the end of the right border (see last capture) if the border color is anything other than black and the intensity of the spike is in direct proportion to the luminance level of the border color - it is about 1/3rd the amplitude. Example: In the last capture, the border is blue and has a luminance level of 200mV above black so the downward spike is about 66mV.
Yeah, I can see that now that you mention it. That one is even stranger. Why would it drop below the black/blanking level in that scenario? The only situation it should drop below that level is during a sync pulse.
eslapion wrote:If you look at the transition from border (blue) to text area (black), there is no spike there so this is specific to the transition from blanking to border and inversely and only if the border color isn't black.
I was interested more in the transition from black to blue within the video matrix part of the screen. I think that would better match the start of the left hand border. But having said this, blue to black would match the end of the right hand border, so the absence of the downward spike is interesting.
It is also very strange that the spike doesn't happen when transitioning from a black border to blanking. That isn't explained by any of my current theories, so could be a key observation for tracking down what is happening.... Although, now that I think about it, there are a number of things different about black that might explain it.
eslapion wrote:I can only assume this is caused by the architecture responsible for activating/deactivating the blanking.
Yeah, it's bit perplexing. I guess we might need to wait to see what the measurements look like for a 6561E, i.e. to match the die shot, since at present I've got the 6561E die shot in my mind and struggling to understand the spikes based on that. In that die shot, black and blanking are equivalent for the purposes of generating the luminance output. Both the blanking and black signals are inputs to the same OR whose output then pulls the luminance to the required value, so in theory there shouldn't be a difference between switching from blanking to blue or from black to blue. - I wonder if it is something to do with timing then? Maybe the blue signal doesn't kick in immediately at the same time as the blanking turns off, and so the luminance level starts getting pulled up momentarily, as there's no pull down at all during that moment, and perhaps the black kicks in quicker.
It doesn't explain why there is a drop at the end of the right border though.
Any chance we might get a 6560 die shot at some point? Would be very interesting for comparison with the 6561E. I've seen at least one web site currently selling them and its a website I trust (as I've used them for other components in the past).