is there a way to detect the pixel clock of one incoming VGA signal.
i'm using the STDI but it can't provide info on the pixel clock.
any way ?
Pixel clock can be derived from knowing what the input format is as shown in UG-214 Table 57. If I know the input is SXGA60 then the pixel clock should be 65MHz. There is no direct way to measure the pixel clock.
I would like to identify the two reduced blanking mode : 1920x1200@60hz and the 1600x1200@60hz.
But this two mode produce the same result for STDI_BL and STDI_LCF and with experience the STDI_LCVS is never the same on different video sources.
And the Hs and Vs polarity is the same.
How to determine the right mode ?
Given a 28.63636MHz crystal, 1600x1200@60 --> BL = 3054 and 1920x1200@60RB --> BL = 3096. What values are you reading?
I'm using the CVT formula because it is recommended for Reduced Blanking mode.
1600x1200@60 RB --> BL = 3094 LCF 1235
1920x1200@60RB --> BL = 3094 LCF 1235
do you think i have to ignore the 1600x1200@60_RB mode ?
For what it's worth, I use the LCV value to differentiate these two modes. My values are:
1600x1200@60RB: BL:3085, LCV:1234, LCV:4, FL:1865
1920x1200@60RB: BL:3085, LCV:1234, LCV:6, FL:1865
First of all 1600x1200@60RB is not a VESA standard, it may fit the CVT formula but it is not listed in VESA DMT spec.
Second if we extrapolate from VESA 1600x1200@120RB to 1600x1200@60RB we get a horizontal clock of 76.2kHz which would give us a BL = 3006, slightly different then 1920x1200@60RB of 3094
If the values are the same then you can not differentiate between the 2 formats.
Using the spreadsheet I have
1600x1200@60RB --> Hor Freq = 74.006kHz --> BL = 8 * 28.636363MHz / 74.006kHz = 3095
1920x1200@60RB --> Hor Freq = 74.038kHz --> BL = 8 * 28.636363MHz / 74.038kHz = 3094
LVC will be the same
Too close to call since the hor freq is almost the same, the only real difference between the 2 formats is the pixel clock which we have no way of measuring.
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