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Display sequence in pattern mode with multiple bit depth,e.g. 8bit

Natty Dale
Prodigy 225 points

Hi there,

What is display sequence  when a 8bit depth  grayscale bitmap is sent to LCr in pattern mode?

Such as in pattern sequence mode, select 8 bitdepth, pattern number is 1, exposuretime is set to 10ms with trigger period set to 0, and a grayscale bitmap with R=80H,G=80H,B=80H is uploaded.

Then i use a photodiode to detect the light output from LCr.

If the Display sequence(as following) in the dlpu004 section 2.3 is right

Then i should see a rectangle wave like this

Instead i see the wave from my oscilloscope as this:

Please be noted that the timescale is 2ms/div.

Can any body explain what the display sequence is inside the LCr?

best regards

-Natty 

  • 0
    TI__Mastermind 30875 points

    Hello Natty,

    About the  'Display Sequence' - You know that the DLP is a PWM type device, each bit is referred to what called as 'bit-plane'. You also know that that every bit has weight called as bit-weight. The MSB bit has highest value and the lowest bit has the least. In your case of the 10ms the 50% of time is allocated for the MSB bit and the next bit  to the MSB gets 50% of the remaining and so on...

    For smooth display instead of displaying the bit-planes in order, the bit-planes are mixed and repeated in such a way that the effective allocated bit weight is still maintained. That is for example - MSB bit  (bit-plane) shown more than once for small amount time (this is called as bit-segment) but when you add the total display time of  MSB bit it will be 50% in your case ~5mSec.

    For the input value of RGB(80H,80H,80H) the MSB bit only needs to be shown, just add all ON time pulses per VSYNC period it will be ~5mSec.

    I hope this explains what you are observing on the oscilloscope.

    Regards,

    Sanjeev

  • 0 in reply to Sanjeev
    Prodigy 225 points

    Hi Sanjeev,

    Thanks.  

    [the bit-planes are mixed and repeated in such a way that the effective allocated bit weight is still maintained.] did explains what i observe. One more question, is there a way to control the mixing algorithm?


    regards

    Natty

  • 0 in reply to Natty Dale
    TI__Mastermind 30875 points

    Hello Natty,

    Yes.

    Unfortunately it is not possible to change. This is how the display sequences are designed. 

    Regards,

    Sanjeev