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External patter monochrome mode

Jakob Wilm
Intellectual 340 points
Other Parts Discussed in Thread: DLPC300

Dear Community,

I need to do fast 8-bit monochrome pattern projection in external mode through HDMI. To that end, I have a couple of questions.

1) Input resolution. In 8-bit RGB mode, I can upload a custom EDID and use e.g. 854x480 which is close to the native DMD aspect ratio, which saves me from doing any interpolation on my own. When changing into 8-bit monochrome mode, any resolution aside from 608x684 seems to fail. Is this expected behaviour, and why?

2) According to the LightCrafter EVM User Guide, in 8-bit monochrome mode, 2 x 60Hz projection frequency can be achieved. Is this correct, and why is it not 3 x 60 Hz? If correct, what is the time slot allocation for the bit planes. Are all mirrors off for a third of the projection period? A timing diagram as shown in Figure 3-3 would be appreciated for monochrome modes.

3) Can exposure times be adjusted in external (HDMI) mode? In this case, is it through command package 0x04 0x00, x04 0x80, or any other?

4) Can trigger delay, polarity, width be configured when operating in external pattern mode (command package 0x04 0x04) ?

Best regards, 

Jakob Wilm, Technical University of Denmark

  • 0
    TI__Mastermind 30875 points

    Hello Jakob,

    Here are the answers to your queries.

    #1. It is expected behavior. 8-bit monochrome mode is 'true' 1:1 pixel:pixel mode. There is no correction to input frame is happening at all in this mode. This mode is useful for applications like 'Structured Light' 3D scanning applications or any other application requiring 'true' representation of 8-bit grayscale input data.

    #2. The 8-bit monochrome display time is explained in DLPC300 I2C Programmer's Guide. Below is the display timing.

    The reason is basically the time required to display a true 8-bit gray-scale value. On DLP LightCrafter to display a perfect 8-bit gray-scale value requires a minimum of 8.333ms. So at 60Hz input it is possible to display just two patterns.

    #3. It is fixed, depends on what is the input frame-rate selected. This topic is discussed in this thread http://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/f/850/p/252132/938032.aspx#938032

    #4. No. The command packets discussed in both #3 and #4 are applicable only for the internal pattern sequence mode.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Intellectual 340 points

    Thank you Sanjeev,

    we hadn't updated our documentation to revision A of the DLPC300 programmer's guide, so thank you very much for pointing us in the right direction.

    Now with respect to the display timing, we are observing the following unexpected behavior on LC. When turning the device directly on and switching to HDMI monochrome 8 bit mode, the image flickers. Presumably every third image is black, but we haven't verified this. Then, when switching to pattern sequence mode, starting a pattern, stopping it and switching back to HDMI, the flicker is gone. Could it be that some state is not set in the first situation? I hope you can reproduce this behavior.

    Regards,

    Jakob

  • 0 in reply to Jakob Wilm
    TI__Mastermind 30875 points

    Hello Jakob,

    I am not able to reproduce the problem you are seeing. 

    What is the resolution and frame rate of the source input? What is the input frame content? Is it some kind of picture or test pattern.

    By default, when you switch to HDMI display mode it will always be running a 'video sequence'.  If you change the Video Mode setting to Bit-Depth = 8, FrameRate = 60 and LED Select = Red/Green/Blue then it will run a '1:1 pixel mode' and displays only 8-bit of Red and Green channels. In either configuration it depends on what is the input frame content is. 

    Some more suggestions -

    Check source properties, how it is detecting DLP LightCrafter as ... what is the detected resolution? If you end application is to operate in monochrome 1:1 pixel mode.. you must set the input source resolution to 608x684. On the Video Mode Setting - LED Select should be non-RGB and appropriate bit-depth and frame rate is selected.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Intellectual 340 points

    Hello Sanjeev,

    I am only operating the LC at 608x684, which is also configured in the EDID, in the LightCrafter, and detected by my computers graphics driver.

    The issue relating to flickering screen in HDMI monochrome mode appears on two different LightCrafters that are on software versions 4.0, 2.6.43, 2.6. It also appears independently of computer and cabling. We have tried two different computers, and the flickering issue appears on both.

    The flickering does NOT occur on our third LightCrafter, which is still on software package 1.1 versions. With exact same settings, cables and hardware, we are seeing a non-flickering HDMI 8bit monochrome output right after boot.

    As I mentioned, we currently resolve this issue by starting a pattern sequence, THEN switching to HDMI. After each reboot, we have to repeat this procedure. As such, we do have a workaround, but still believe there is an issue relating to the latest firmwares.

    Regards,

    Jakob Wilm

  • 0 in reply to Jakob Wilm
    TI__Mastermind 30875 points

    Hello Jakob,

    Yes. It is a bug got introduced in the new build. Thanks for pointing it out. We will fix it in next major release. 

    Your workaround looks proper to me. 

    Regards,

    Sanjeev

     

  • 0 in reply to Sanjeev
    Intellectual 340 points

    Hi Sanjeev, 

    after investigating further into 8 bit monochrome projection via HDMI, I discovered the following peculiarity:

    Selecting 8-bit 45Hz monochrome HDMI mode result in an unexpected trigger output. I do not know about the exposure pattern, as I haven't hooked up a phototransistor to my Oscilloscope. The DLP300 Programming Guide would suggest a regular trigger output as shown below, regardless of selected framerate:

    However, what I get on the trigger output is the following:

    Is this another bug?

    Best regards,

    Jakob

  • 0 in reply to Jakob Wilm
    TI__Mastermind 30875 points

    Hello Jakob,

    Let me know input frame-rate at the HDMI port. It should matches to the selected sequence frame-rate. In your case it should 45Hz. By giving frame-rate < 45Hz cause the sequence to abort in the middle as it receives new VYSNC input before completing the current pattern exposure. 

    Regards,

    Sanjeev