Crystal Frequency

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1

Dear all,

I am working to interface an ARM to my QVGA TFT LCD. I was just wondering how I can determine the crystal for the ARM. I am wondering how fast should I update the fill the frame buffer that the LCD is not slowly growing?

I do appreciate for your time in advance,

John.

2

your questions aren’t even a beginner type.

3

Dear lisarden,

I was just wondering if you did understand my question. Anyhow let me repeat it here again. I am wondering how fast one should fill up the full buffer of a LCD driver without seeing the display growing up slowly. On the other hand you would like to see the image will be displayed abruptly.

Thanks,

John.

4

Do you know what PLL is?

5

No, not really. Would you mind to explain it to me.

High Regards,

John.

6

By PLL do you mean phase lock loop?

Thanks,

John.

7

The crystal frequency is 12MHZ. The Processor clock can be as high as 720MHZ depending on what you set it for. There are dozens of clocks inside the processor, all generated by, a PLL, a device that generates higher frequencies from a lower frequency.

The clock for the LCD interface can be set totally independent. Your question has nothing to with the processor clock frequency. Look at reading up on the processor’s LCD section.

http://www.ti.com/product/am3359

Gerald

8

Thank you Gerald for the info. What is the minimum time required to fill the LCD without small growing data on the LCD. Would it be correct in order for eye not to distinguish the slow write the whole LCD should be updated at most 16.5ms. Am I correct please?

Thanks,

John.

9

If you really want to know a frequency number (i don’t know how you should use this info though) just multiply the frames per second by the pixels on a frame (depending on the resolution).
Say you want 60 fps on 1024x768 (786432 pixels per frame), so you have 786432*60 pixels per second = 47185920 pixels per second.