problem of LPC1788 driver 7" tft lcd

[lpcware]

Content originally posted in LPCWare by hujiafu on Fri Mar 18 02:41:13 MST 2016
my Environmental is LPC1788 CCLK@108MHz, PCLK@54MHz, EMCCLK@54MHz, SDRAM is 32bit width
when I driver a 4.3" TFT LCD(480*272) LCD_DCLK is 6MHz, the wave of LCD_DCLK is OK, also the LCD is display fine
but when I driver a 7" TFT LCD (800*480) LCD_DCLK is 36MHz(CCLK/3), the wave of LCD_DCLK range is so small.
follow is a pictrue of LCD_DCLK (36MHz), range from 1.8V - 2.8V,
Can any one help me,
Thank you!!!

[lpcware]

bump

[lpcware]

Content originally posted in LPCWare by hujiafu on Thu Mar 24 05:32:38 MST 2016
Thank you every one, my problem is fixed.

my oscilloscope has some problem, my LCD is not support the VS and HS ,but only support DE.
:)

[lpcware]

Content originally posted in LPCWare by hujiafu on Fri Mar 18 18:47:52 MST 2016
1. My oscilloscope bandwidth is 100MHz.

2. There is no series reistor in the LCD_DCLK wire. how mush the series resistor value need ?

3. I measured the wire both connected LCD and none connected LCD, the wave is no change in the oscilloscope.

[lpcware]

Content originally posted in LPCWare by wmues on Fri Mar 18 09:03:09 MST 2016
How much is the bandwidth of your oscilloscope?

Is there a series resistor in the LCD_DCLK wire?

Is there a capacitor at the input of the LCD_DCLK on the LCD?

[lpcware]

Content originally posted in LPCWare by hujiafu on Fri Mar 18 07:03:23 MST 2016
Yes, I did set slew flag for this pin (LCD_DCLK P[2.2]), but it's no change when I measuiring the signal

* Type D pins (digital pins)
   */
  #define LPC178X_GPIO_CONFIG_D(func,mode,hys,inv,slew,od) \
          ((func << LPC178X_GPIO_CONFIG_FUNC_BITS) | \
          (mode  << LPC178X_GPIO_CONFIG_MODE_BITS) | \
          (hys   << LPC178X_GPIO_CONFIG_HYS_BIT  ) | \
          (inv   << LPC178X_GPIO_CONFIG_INV_BIT  ) | \
          (slew  << LPC178X_GPIO_CONFIG_SLEW_BIT ) | \
          (od    << LPC178X_GPIO_CONFIG_OD_BITS  ))


/* P2.2 (D) = LCDDCLK */
{{2,  2}, LPC178X_GPIO_CONFIG_D(7, LPC178X_NO_PULLUP, 0, 0, 1, 0)},[/color]

In LPC178X User's Manual, It has writed Slew rate control is disable. This mode reduces the output delay by 1 ns compared to the standard mode.
It's only 1 ns faster than standard mode. so it's not a key point for the waves.

[lpcware]

Content originally posted in LPCWare by mc on Fri Mar 18 06:38:48 MST 2016
Hi,
Did you enable fast slew rate in your code? It may improve signal.