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TFP410 DE generator basic question

cobsonchael
Mastermind 7930 points
Other Parts Discussed in Thread: TFP410

so the datasheet for this part isn't clear on some stuff for me and i'm still wet behind the ears with this part so bear with me.

the DE generator is a little confusing as to what it really does.

i understand it handles the data enable state for the system so if there is no DE signal going into this thing you can still write to the panel.  if i am wrong on that please correct me.

one thing that it looks like it might also do is handle positioning the image on a bigger screen so your oddball image (say 1024x600) can sit in the middle of a 1280x720 screen. is that right? is that the point of the DE_TOP and DE_DLY? it would make sense based on my interpretation of the graphic on page 16 of the datasheet. the main screen is in the middle surrounded by a black border that is DE_DLY and DE_TOP many pixels big...right? if i am wrong then what is the true purpose of DLY and TOP?

also my question on the V_RES and H_RES values.   one thought i had was that they represent the pixel height and width of the image you are trying to output, right? but they are not the pixel dimensions of the image i am actually putting out there so it makes me think these numbers represent the biggest i can get using this configuration? are one these ideas right? if they represent the biggest i can output then are the values adjustable if i change clock frequencies?

  • 0
    TI__Intellectual 1805 points
    Hi Cobsonchael,

    DE generator generate DE signal if the video source doesn't provide it. DE signal it is used to make difference between active video and blanking period, so DE is high while active video is being transmitted and low while the rest of the transmission. This way, DE_CNT and DE_LIN correspond to the actual resolution of the panel, and DE_TOP and DE_DLY to the blanking period.

    Regards,
    Aldo.
  • 0 in reply to Aldo Acero
    Mastermind 7930 points
    so me being a newbie...

    how does the blanking period relate to the system? is that something that is related to the data being sent out (front porch, back porch values) or is it dependant on the panel being sent to? or is this something that, like i asked before, can be using to put an odd resolution on a standard display size? and also how does H_RES and V_RES relate to all of this. what are those values used for?
  • 0 in reply to cobsonchael
    TI__Guru* 76130 points
    Hello,

    When a sink is connected to a video source, the Source reads the EDID data from the Sink, this data contains the resolutions that the Sink(display) can work with, based on this information the Source(graphics processor) decides what resolution it is going to send to the Sink.

    The DVI specs defines the "active area" and the "blanking area", the active area is where the videos is being sent and the blanking refers as you said to the front porch, back porch.

    When for some reason the Source is not able or capable of defining the active and blanking areas, the TFP410 is equipped with a DE generator to do that, in this way, the values you set to the DE Generator Registers will define the active and blanking areas.
    You will have to know what are going to be the supported resolution of the Sink in order to program the correct values for the DE Generator.
    Regards
  • 0 in reply to Elias Villegas M.
    Mastermind 7930 points

    when the EDID data gives me the number of blanking pixels/lines it also gives me the front porch, but it can't find anywhere where it gives me the back porch. it looks like i am to find the front porch, and pulse width and from that calculate the back porch from the blanking interval. is that right? 

  • 0 in reply to cobsonchael
    TI__Guru* 76130 points
    Hello,

    Not exactly, it is not standard, every display can have different values for front and back porch, the display's datasheet should specify how many pixels correspond to each porch.
    Regards