Cannot drive LightCrafter 4500 with 120 Hz signal, stuck at 60 Hz

A few additional details that have come up:

• By setting up "custom resolutions" in the Nvidia control panel, I can force video output to 120 Hz, either at 1280x800 or 800x600. Static rendering looks qualitatively normal, and video playback is qualitatively smooth. This works over all graphics card outputs (DVI, HDMI, DP).
• However, at 120 Hz, the mouse position is updated abnormally slowly, so it looks and feels choppy. Adjusting any potentially relevant settings (e.g. Vsync) in the Nvidia control panel doesn't do anything noticeable - still choppy. I've tried a bunch of different mice - all show the same problem.
• Also, there appears to be a scaling issue: at 800x600 @ 60 Hz, the "screen" only occupies the central portion of the DMD. At 800x600 @ 120 Hz, the "screen" is expanded to fill as much of the DMD as possible, while maintaining aspect ratio.
• The EDID from the registry does not have any mention of 120 Hz at all.
• The LightCrafter 4500 shows up in the Device Manager as a PnP Generic Monitor.

Is any of this expected behavior? It seems like the LightCrafter 4500's native 120 Hz cabability is not in the EDID, and it seems like the custom 120 Hz resolution is causing problems independent of this...

Many thanks,

Jonathan

Hello Jonathan,

You are correct, there is NO 120Hz signal timing stored in the EDID. 

Could you please let us know your plan of 4500 Kit, do you plan to use it as basic video projector? If it is so then you can input 1280x800 WXGA resolution at 120Hz. 

Couple of very important factors, supported max pixel clock 150MHz, there is minimum vsync and hsync configuration, it is defined in DLPC350 datasheet, Table 11. Source Input Blanking Requirements. 

If you care about driving the Kit in native resolution to get 1:1 output then you must generate video at 912x1140 resolution video. 

Regards,

Sanjeev

Hi Sanjeev,

Thanks for your response. Here's a little bit more about my application.

I'm sending OpenGL animation to the LC4500 via HDMI. I need single LED monochrome (e.g. only blue, every frame). I need to update at around 200 Hz or greater. Bit depth should be >= 6 bpp. It would be better if I had pixel accuracy, but as long as I get fast frame rate and true monochrome, I'm basically okay.

In video mode, I can generate normal 24 bit "RGB" signal at 60 Hz, and I can turn off red and green LEDs manually so I use only blue. In this way, the R, G, and B subframes of each 24 bit RGB frame each become a single 8 bit blue frame. This should give me 180 Hz monochrome, with 8 bpp. Is this correct? I realize that the subframes will be different durations - this is okay.

Incidentally, how does one determine subframe durations for video mode? In general, how does one determine what image processing is being applied?

I believe I should also be able to do similarly while generating 24 bit RGB signal at 120 Hz. However, I cannot get the LC4500 to present 120 Hz signal correctly at any resolution. If there is no 120 Hz timing stored in the EDID, is the recommended way of achieving 120 Hz through custom resolution/timing settings?

In pattern mode, I'd like to use video port and vsync triggering. Again I send a 24 bit "RGB" signal at 120 Hz. Each 8 bit subframe is then rendered as a separate 8 bit monochrome frame by appropriate pattern sequence configuration. Hence, every ~8 ms, the computer sends 1 x 24 bit RGB frame, which gets split into 3 x 8 bit blue frames that are presented in the pattern sequence. Something like: vsync - F0 (G0-G7) - F1 (R0-R7) - F2 (B0-B7). This should give 360 Hz.

However, this does not appear to be consistent with the user's guide, which suggests that the maximum update rate for 8 bit frames is only 120 Hz. See http://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/f/924/t/279228.aspx for further discussion. If it's true that 8 bit frames can only be presented at 120 Hz, and I am sending the LC 4500 24 bits of data every ~8 ms, what happens to the 16 bits of data per RGB frame that are not presented?

If it's necessary to send a lower bit depth signal in order to achieve higher frame rates, could you direct me to an example of how to form such a signal, and how to configure the graphics card to transmit it appropriately?

Thanks for your help,

Jonathan

In video mode, I can generate normal 24 bit "RGB" signal at 60 Hz, and I can turn off red and green LEDs manually so I use only blue. In this way, the R, G, and B subframes of each 24 bit RGB frame each become a single 8 bit blue frame. This should give me 180 Hz monochrome, with 8 bpp. Is this correct? I realize that the subframes will be different durations - this is okay.

[Sanjeev] Unfortunately it is not correct. In the Video Mode the 60Hz duration split across Red, Green and Blue channels, turning off of Red and Green channels means only the LEDs are OFF the DMD still continue to use the allocated time. In other words blue channel pattern display rate is still at 60Hz. And the display time as i said only 20% of 16.67ms for blue.

Incidentally, how does one determine subframe durations for video mode? In general, how does one determine what image processing is being applied?

[Sanjeev] Duty cycle number, it is fixed, R 35%, Green 45% and Blue 20%. 

I believe I should also be able to do similarly while generating 24 bit RGB signal at 120 Hz. However, I cannot get the LC4500 to present 120 Hz signal correctly at any resolution. If there is no 120 Hz timing stored in the EDID, is the recommended way of achieving 120 Hz through custom resolution/timing settings?

[Sanjeev] Just input WGXA resolution source at 120Hz, it should lock and display properly. Again the minimum front-porch and back-porch of HSYNC and VSYNC signals is listed in DLPC350 Datasheet.

In pattern mode, I'd like to use video port and vsync triggering. Again I send a 24 bit "RGB" signal at 120 Hz. Each 8 bit subframe is then rendered as a separate 8 bit monochrome frame by appropriate pattern sequence configuration. Hence, every ~8 ms, the computer sends 1 x 24 bit RGB frame, which gets split into 3 x 8 bit blue frames that are presented in the pattern sequence. Something like: vsync - F0 (G0-G7) - F1 (R0-R7) - F2 (B0-B7). This should give 360 Hz.

[Sanjeev] Video Mode - Blue channel display period still remains at 120Hz only. I have answered in the first question.

However, this does not appear to be consistent with the user's guide, which suggests that the maximum update rate for 8 bit frames is only 120 Hz. See http://e2e.ti.com/support/dlp__mems_micro-electro-mechanical_systems/f/924/t/279228.aspx for further discussion. If it's true that 8 bit frames can only be presented at 120 Hz, and I am sending the LC 4500 24 bits of data every ~8 ms, what happens to the 16 bits of data per RGB frame that are not presented?

[Sanjeev]  Fundamental thing about DLP4500 display; on a non-VideoMode or Pattern Display Mode, when we say 8-bit grayscale display; basically the DLP needs 8.334ms of time.

Suppose you are running at 120Hz video signal input to RGB parallel port, since we know that DLP takes 8.334ms of time to generate accurate 8-bit gray scale value, there is no way it is possible to display other 16bit, it also means those 16bit never going to be addressed. 

Which of the 16-bits not addressed? This is strictly controlled by Pattern Number selection, refer to DLPC350 programmer's guide, Table 2-66. Pattern Number Mapping, for 8-bit, possible number are 0,1,2. 

If it's necessary to send a lower bit depth signal in order to achieve higher frame rates, could you direct me to an example of how to form such a signal, and how to configure the graphics card to transmit it appropriately?

[Sanjeev] OK. I think the best you can do taking 120Hz input VSYNC and lower bit depth would be try 6-bit depth pattern display mode. 

So, incoming video = 120Hz, 8.33ms

6-bit display time = 2.5ms

so you can display 8.33/2,55 ~ 3 times, the effective refresh rate you could achieve, 360Hz 6-bit.

About generating the patterns, since the input payload is RGB24bit frame, you need to pack, 3 pattern data, refer to DLPC350 Programmer's Guide, Table 2-66, 6-bit column, chose 1st three pattern numbers 0,1,2, leave 3 because you don't have enough time to display the 4th one in available 8.33ms.

RGB24 bit data - 

G5:0            - 6-bit Pattern#1 

R3:0G7G6  - 6-bit Pattern#2

B1:0R7:R4 - 6-bit Pattern#3

************************************

Another option

************************************

Set Input rate to about 98Hz, then you can display all the 4 6-bit patterns from the incoming RGB24bit frame, in this case the effective refresh rate goes upto 392Hz.

Regards,

Sanjeev

Hi Sanjeev,

I too like Jonathan have a Lightcrafter 4500 and am unable to drive it at 120Hz. The projector is connected to an Nvidia Quadro K5000 graphic card which is capable of achieving that refresh rate. When I try to manually set a custom resolution/refresh rate in nvidia's settings, I am presented with the following screen. You mentioned that the timing values are in the linked document, but we seem to be unable to decipher the right values. Could you please let us know what numbers are we to enter in the timing section to get the refresh rate up to 120Hz.

Hopefully, once we have this set up we can attempt to increase the rate with pattern mode settings in the lightcrafter gui.

Many thanks,

Dhruv

Hello Dhruv,

Couple of questions to you - 

1. I believe without any custom adjustments, with this graphics card, the LightCrafter4500 kit is able to lock the signal perfectly at 1280x800@60Hz. Is this correct?

2. Now you are attempting with custom resolutions, 1280x800 @120Hz, you settings look OK to me. When you click on the Test button, isn't  the DLP4500 Kit locking to the video signal? Let me know what you are seeing.

By the way for this exercise ensure the display mode is Video Mode. 

Regards,

Sanjeev

Hi Sanjeev,

You are correct, the LC works great at 1280x800 at 60Hz.

When we attempt to set the refresh rate to 120Hz (with CVT reduced blank), the test is successful and the windows desktop appears. The problem however seems to be with the refresh rate, mouse movement is choppy and skips frames, video playback is not smooth. It appears as if the refresh rate has dropped below 60Hz.

Thanks,

Dhruv 

Thanks Sanjeev. Sent you a friend request, I can explain in more detail then. 

Dhruv