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Helligkeiten der C64 PAL-Palette - zum 100. Mal

  • On an 8565R2 the color burst amplitude in the composite signal appears to be 0.15V - exactly what it should be by the PAL standard. Then all the colors also have this 0.15V amplitude.

    On 6561R5 the color burst starts off at about 0.15 - 0.16 V, then drops to 0.12 - 0.13 as the chip (and/or modulator?) gets hot. The color amplitudes are about 1.1 - 1.3 times that of the color burst. So in theory the 6561 should look slightly more saturated, but I'm not sure if it is noticeable.

    On 8565R2 the color amplitude appears to remain constant as things heat up.


    May I add that the resulting saturation is not strictly equivalent to the color amplitude but relative to the burst amplitude and for a given luminance...and also the result of the subcarrier deviation of adjacent lines ?!

    Visually, a composite vectorscope display including a burst measurement bar will deliver the information in the best understandable way, IMHO.


    I had some thought about the absolute signals. I was driven to know how to calculate the sqrt (U²+V²) "vector" out if the voltage reading of the color signal. I (think that I) understood much more about the video signals than I ever wanted to know.8o Please view attached the PDF about the current uncertainties.


    mathop  silverdr  ius

    I think that you are experts and might have some answers.:saint:


    silverdr

    For the already done measurements, can you please add the information for composite syn/blanking/black absolute voltages & color burst amplitude, and for separate video the color burst amplitude?
    It might help us to put the measured values in the right relation.


    Thanks!:saint:

  • Got a bit busy at work, so did not get to look at the sheet details yet, sorry.

    I got a 250407 rev A board recently so I can do some 6569R1 measurements now also.

    No worry mate. It's a hobby, so no rush.
    6569R1 measurments would be really cool. At the momement, we just assume that the colors are same as other NMOS.

    I think we can define the hues very precisely meanwhile.

  • Luma voltages on my 250407 board, with the 6569R1: (75 Ohm termination)


    Code
    1. cold hot
    2. sync -0.22 -0.27
    3. black 0.00 0.00
    4. red/blue/brown/dark_grey 0.13 0.15
    5. purple/green/orange/light_red/grey/light_blue 0.29 0.34
    6. cyan/yellow/light_green/light_grey 0.44 0.51
    7. white 0.61 0.68

    'hot' = after about 1 hour


    Input was AC coupled, so I adjusted the voltage to make black equal to 0V.

    I did not want to mess about with the board so I did not do the resistance measurements.


    I believe this board still has the original modulator (without SMD parts.). On composite video the color signal is almost nonexisting, I had to set saturation to the maximum level on my capture card and then it still looked slightly under-saturated. Also I can't appear to get consistent angle readings. I guess I don't have the proper equipment to do this. Or the color signal is just bad.


    Color angles appear to be, roughly,


    Again, these should be taken with some grains of salt. Also I may have even/odd mixed up, I can never tell which is which. These angles appear to match the 6569R3 and 6569R5 chips.

  • Thanks mathop ,

    much appreciated.


    The data looks as we expected I would say

    Input was AC coupled, so I adjusted the voltage to make black equal to 0V.

    But on the C64 outputs, if I would measure a veeeeery slow greyscale signal (composite vid and separate vid luminance) with a voltmeter, I would get "real" voltages between ~0...1V, correct? (with that 75 Ohm termination of course)

    I believe this board still has the original modulator (without SMD parts.). On composite video the color signal is almost nonexisting, I had to set saturation to the maximum level on my capture card and then it still looked slightly under-saturated. Also I can't appear to get consistent angle readings. I guess I don't have the proper equipment to do this. Or the color signal is just bad.

    Do you think this is some defect on the board or 6569R1 unique?
    You don't have a device to measure color burst and color amplituted, right?
    Anyway, the color angles' result doesnt' look bad at all.:thumbsup:

    Again, these should be taken with some grains of salt. Also I may have even/odd mixed up, I can never tell which is which. These angles appear to match the 6569R3 and 6569R5 chips.

    Indeed I guess you mixed odd/even, ;) But doesn't matter really.
    Here are the results.

  • Did some more detailed measurement of the color angles on various boards.

    Looks like 6561R3 and 6561R5 are more or less the same. The 6561R1 would probably also look like this, but I don't have that chip.

    The color generator was redone in the 8565 so there the angles are also significantly different.

    What's interesting is that in the 8565 the odd/even value for brown are the same, and the even angle for yellow is less than the odd angle (for all other colors it is the other way around.)

    board1 - 6569R5 with stock modulator

    board2 - 6569R5 with butchered modulator (no RF bits)

    board3 - 6569R3 with stock modulator

    board4 - 8565R2 with stock modulator


    mathop

    Are board1 and board2 identical to the ones you already used for your palettes?
    http://www.michiel.boland.org/c64_colors.html


    Do you know assy number of the other boards?

    Thanks!

  • Yes, those are the same boards.

    Board3 is also a 250425, but a rev B (board2 was rev A)

    Board4 is a 250469 rev 4

    And then now we also have board5 which is a 250407 rev A

    I guess I have too many C64s now. :)

    I should point out that at least for the 6569R1 (i.e. board 5), the luma voltages for individual colors also depend on the overall picture. For example, if you make the border white you get lower voltages than you would get if you make the border black.

    But since the sync-black voltage also gets lower, I don't think this will affect the picture on a monitor.


    For example, if you adjust output voltages so that sync-black is at .3V you get something like this (vertical resolution is 0.004V)

    Also see attached images - these are the color bars I used for measuring on the oscilloscope

  • Interesting, I will check it. So this board not only needs warming up, it also depends on the border. Strange board.:P

    What is the "corrected" value here?


    Also see attached images - these are the color bars I used for measuring on the oscilloscope

    Can you also measure the color burst amplitude of the compostie signal of those boards and the colors' amplitudes?
    Both should be around +-150mV
    To define somehow which saturation we will use for the palettes. But I guess it will be 0.215 (=150mV), except for the brown to stay within the RGB gammut.

  • The "corrected" voltage is 0.30 * V / sync_depth (so the corrected sync depth then is 0.30 by definition.)


    E.g. for the first red you get

    0.30 * 0.132 / 0.232 = 0.171 which is then rounded to 0.17

    (only the first two digits are accurate)


    The color amplitudes on the 6569R1 are


    I hope I have the even/odd correct this time :)

    Angle is approximate, I used some python hacking to process the scope CSV output.

    Color burst amplitude appears to differ between lines, not sure what is going on there.

  • Forgot to mention, table above was from the Y/C output.

    Below are color amplitude and angles from the composite output

    As noted earlier, color signal on composite output is very faint.

  • Forgot to mention, table above was from the Y/C output.

    Below are color amplitude and angles from the composite output

    As noted earlier, color signal on composite output is very faint.

    What means burst-1 and burst-2?


    Amplitude of 0.32 means +-0.160 mV, correct?


    Did you connect the composite output to a TV/monitor? Also no color exsiting on the display?


    For the Chroma output, I would expect a much higher voltage. I think you also measured +-500mV:

    http://www.michiel.boland.org/c64_colors/luma_colors.txt


    Or did you adjust saturation or something?

  • The last two measurements are from my oscilloscope, not the capture card.

    I capture two lines of color bars in my scope, so one of them is even and the other one is odd, burst-1 and burst-2 are just the first and second color burst signals. Then I import the CSV data off the scope into a local python script. That uses some heuristics to determine the phase of the color carrier, then extract the U and V signals, and calculates the color amplitude based on those. I verified the python script on a known good set of color bars (raspberry pi composite output) so I know it sort of works. :) This is all a bit of a work in progress.


    To get the peak-to-peak voltage for the color signal you need to multiply amplitude by 2.

  • I capture two lines of color bars in my scope, so one of them is even and the other one is odd, burst-1 and burst-2 are just the first and second color burst signals.

    burst-1 is odd and burst-2 is even or they are just any, means as a reference, we can avg both?

    To get the peak-to-peak voltage for the color signal you need to multiply amplitude by 2.

    So the max. peak-to-peak value is 0.33x2= 660 mV here in the Chroma line?

    It was about 1000 mV in your 6569R5 measurements, correct?

  • burst-1 is odd and burst-2 is even or they are just any, means as a reference, we can avg both?

    So the max. peak-to-peak value is 0.33x2= 660 mV here in the Chroma line?

    It was about 1000 mV in your 6569R5 measurements, correct?

    I trigger on falling edge of luma to catch the hsync pulse, then burst-1 is the burst that occurred on the line before the trigger, and burst-2 is the burst after the trigger. The trigger is random, so burst-1 may be on a even line and burst-2 on an odd line or the other way around. I guess the naming is a bit unfortunate here. :)


    1000mV max chroma p-p on 6569R5 is correct I believe, at least for my board.


    I think it is not the absolute amplitude that matters, rather the amplitude relative to that of the color burst.

    On C64C the amplitudes are all the same, so that makes things easier there.

  • I think it is not the absolute amplitude that matters, rather the amplitude relative to that of the color burst.

    Maybe. I am not a TV engineer. ;) According to the standard, the reference for color burst is +-21.5 IRE. Which is +-150mV. 300mV p-p
    If the TV input section scales the colors's amplitudes according to the ref._color_burst/act._color_burst ratio, you are correct. Just a question if any TV will act similar and how much OFF-standard it will compensate.:whistling:

    I am just wondering that the chroma absolute outputs are that different. On your 6569R1 board, it's 660 mV p-p, on the 6569R5 it was 1040 mV p-p. Standard allows a max of ~885mV p-p for a full saturation.
    Just want to understand about that magic 330 Ohm resistor people are using to somehow reduce the spicyness of the chroma line.

    On C64C the amplitudes are all the same, so that makes things easier there.

    Almost same yes. ;)
    Already from your capture card palettes for the 6569R5, I could see that the color amplitude swings around +-10% from an avg value, depending how far the color angle is off from the target angle.
    From silverdr measurements, I could see a similar swing, but the amplitude of the swing is just +-1% for the 8565R2.

  • The VIC-II chip does not output true sine waves. The newer modulators have a low-pass filter in the chroma input that resonates at the color carrier frequency. That will make the color signal look more like a sine wave. As far as I can tell the original modulator did not have this filter.

    One theory could be that the resonance in the filter also increases the output voltage.


    I made a 'chroma-only' capture of all boards with the luma signal fixed at halfway between black and white. Here you can see that the 6569R1 color signal is very bad, compared to the others. Also the c0pperdragon modulator signal does not look quite right, that also does not have an input filter. Color signal was sampled at 2 times the color carrier frequency, which might explain the checkerboard patterns here. Sampled picture is also scaled by 8.