Increase LCD refresh rate using iMXRT1064 for 7" display

[anujtanksali]

Hello,

How can i increase the LCD refresh rate. I am trying to increase the LCDIF_CLK_ROOT in clocks configuration in MCUXpresso config tools. is my understanding correct? Will this increase the LCD refresh rate

if yes then It is not allowing me to set a clock greater than 75MHz. Currently it is 67.5 MHz

I am using 7" TFT LCD with 800x480 resolution 565 RGB mode and Emwin graphical library on iMXRT1064 device.

On my hardware i see a faint flickering. How can i avoid this? 

using emwin memdev api or multibuffering does not seem to resolve the issue.

Thanks

Regards,

Anuj Tanksali

[jeremyzhou]

Hi Anuj Tanksali,

Thank you for your interest in NXP Semiconductor products and
for the opportunity to serve you.
1) To provide the fastest possible support, I'd highly recommend you to refer to the application note:
https://www.nxp.com/docs/en/application-note/AN12302.pdf to learn how to adapt the refresh rate.
2) How can I avoid this?
-- I guess it may be related to the hardware circuit, whether the faint flickering still happens when the LCD refresh rate decreases.

Have a great day,
TIC

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[anujtanksali]

Hello jeremyzhou‌,

Thank you for your reply.

The document is very helpful in understanding the LCD parameters.

As per the calculation mentioned in the document shared the CLK comes to around 33MHz and same is given as the typical LCD freq in LCD datasheet and max freq for the LCD is 38 MHz

I was able to check the LCD with DOT clock changed to 33 MHz and 38 MHz but in both cases no change in flickering observed.

Are there any Emwin configuration options which can be tried? I see there are options to use muti-buffering and Memdev

Will these options reduce the flickering?

Any other parameters i can change and check?

Thanks

Regards,

Anuj

[jeremyzhou]

Hi Anuj Tanksali,

Thanks for your reply,
I was wondering if you can introduce some background information about the flickering, such as when it will happen, what it looks like. etc.
And I'll appreciated if you can attached the picture of the flckering.
In further, I'd like to suggest you to  run the elcdif demos (from the SDK library) for testing and to check whether this flickering will happen or not.

Have a great day,
TIC

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[anujtanksali]

Hi jeremyzhou‌,

Thank you for your reply.

I have some observations.

I am able to control the backlight brightness through PWM signal. Reduced the brightness a little with duty cycle 60%.

The flicker seems to reduce a lot due to this. I varied the duty cycle from 50% to 100% and observed that the flicker is observed at higher duty cycles i.e. above 80%. 

So am confused whether it is really a flicker problem or due to reduction in brightness the flicker is not visible.

Do you have any inputs regarding my observations. 

In the meanwhile i will see if i can run the emwin demo on my board and send you the video so that you will get an idea about the flicker.

Thanks

Regards,

Anuj

[anujtanksali]

Hello jeremyzhou‌,

I was able to resolve the flicker issue. 

I had to reduce the LCD dot clock to 33 Mhz as per the calculation in your shared document. 

But the main root cause for the flicker was the above commented function. I had to comment above function. 

As i was changing the LCD settings in clock config the above highlighted function would overwrite any LCD divider and clock settings done through clock config.

Thanks

Regards,

Anuj

[carstengroen]

Thats why 1 measurement is always better than 1 assumption :smileywink: