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STM32F439NI 1V DC biased LCD clock

Question asked by kim.chris.001 on Oct 30, 2017
Latest reply on Oct 30, 2017 by kim.chris.001

Hi ST and Folks.

 

I found a strange point on STM32F439NI LCD clock.

When I set LCD clock to 33.25Mhz, the clock goes up around 1V like DC bias and peak to peak becomes 2V.

However, in cases of under 20Mhz such like 16Mhz, 8Mhz, there is no problem. I mean the clock starts 0V and

goes to 3.3V.

 

The reason why I am seeing this is my LCD screen is broken with 33Mhz (actually over around 20MHz)

but there isn't any problem with 16Mhz and 8Mhz.

 

When I captured the strange clock signal, LCD clock pin doesn't connect to anything and I pick oscilloscope probe

on actual STM32F439NI LCD clock pin (H3).

 

Could you please anybody if this clock signal(1V dc biased) is normal or not?

If not, what can cause this problem? Thanks in advance. Chris

 

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