LCD debugging FAQ and precautions

Functions: init, sleepin, sleepout, displayon, and displayoff
Note:
In LCD debugging, latency is particularly important. It is necessary to determine that the extended time is sufficient, especially when the delay following the voltage register is changed. I remember that there was a phenomenon of screen jitter and I couldn't find out the cause. The manufacturer sent two people from Japan and did not solve the problem. Finally, I tested all the time series and found that the delay was insufficient, A function transmission parameter that affects latency is incorrect.
1. A delay (about 10 ms) is required before initialization to ensure reset stability;
2. If the screen is blurred, the speed of the bus may be high;
3. If the screen flashing is obvious, you can adjust the voltage to stabilize. Generally, the adjusted voltage is VRL, Vrh, vdv, and VCM. These voltages can also be used to adjust the bright and dark (contrast );
4. When you adjust the contrast, you can also adjust the GAMMA value. The objects to be adjusted are: GP, PRN, VRP, VRN, etc;
5. Note that when the data is 8-bit or 16-bit, pay attention to the changes when writing commands and data functions;
6. If the brightness of the LCD is found to be faulty during debugging, check (consider) whether the current provided to the LCD is consistent, and then adjust the voltage.
7. The simplest way to handle the screen flushing problem is to add a black screen flushing function at the end of init. You can also add a latency function to the sleep function;
8. If there is a random white screen problem, one may be the static electricity problem. Take the LCD to the hair and wipe it a few times. If it is easy to have a white screen, it is definitely the static electricity problem. In the case of backend IC, it is also possible that bypass is not handled properly.
9. I also encountered a problem. When I wrote the PLL register twice, the screen Jitter was very high. This problem should be related to the internal implementation of the LCD, not every one of them will.
10. Horizontal jitter. You can't see the screen clearly. Modify the entry mode.
11. If the font is reversed, modify drive output control, GS, and SS;
12. If the font above the image is refreshed to the bottom, the area is not refreshed properly;
13. If the image is displayed separately, the starting point is not at the origin. Most of them are full screen refresh. The starting point register is not set;
14. DMA refresh method. Each refresh is a row. Only one row can be refreshed at a time. Otherwise, errors may occur, reducing the cycle computing time, improving the LCD refresh speed, and reducing the response time;

Online materials:
Today, LCD is triggered by the following problem: when an image is displayed, there may be some highlights in the light and shade color transition, and sometimes the image is still flashing constantly. Who has encountered such a problem? Is it hardware problems or software adjustable?
I adjusted the pixel clock polarity and changed it from the rising edge sampling to the falling edge sampling. I don't know what's going on.
2. What are the common problems with water ripple in LCD?
Short signal to the ground, you can check whether the Board is affected, such as power supply or crystal oscillator, and whether the signal line you output to the LCD is going wrong, check whether the power supply and backlight voltage have ripple. Check whether the resistance, capacitance, and voltage of the peripheral LCD circuit are clean.
This is mainly because the right side can appear in the close when the signal is input, there is a signal reflection or pulling between the signal line, the ground line and the signal line; there is also a situation that the camera control IC is unstable, the output control signal is unstable or hairy
1. Ripple Output by the backlight chip: Check the charge pump (DC-DC) circuit and replace it with an appropriate filter capacitor;

2. LCD Driver power management:

(1) ensure that there is sufficient time delay between chargepump and chargepump levels. This should be adjusted for different systems;

(2) the output end of chargepump must have a large enough filter capacitor.

3. Modify the driver mainly for the display cycle registers.

It must be a problem with the backlight power module. It is estimated that you are using the PWM method to control the brightness of the screen!

The reason for this ripple is that the frequency difference between the LCD screen flushing frequency and the white light is less than 20Hz, just like watching the high-speed rotating fan Leaves Under the fluorescent lamp! A good solution, software needs to adjust the PWM frequency, good luck can solve the problem, if the LCD brush frequency is not very stable, it will not be able to solve the problem 100%
Problems with LCD stripes:

1. The width of the stripe. A Wider stripe is generally related to the backlight.
2. When the LCD is shaking, the line-by-line scanning is obvious due to the angle change. This is related to some driver IC and can only be optimized by modifying parameters.
3. The parameters are not properly debugged, and the scanning frequency and the voltage of the driving columns are involved!

4 mobile phone LCD & camera ESD Problems
Air Display, standalone (isolated), preview mode (camera on)
The mobile phone is a single board (not a folding or slide cover)
If the mobile phone screen is up, +-10 kV pass;
But the mobile phone is down, +-3 kV will be shown
There is still no problem if you try to push the phone down to a certain distance from the desktop. If you want to do so, find the discharge circuit. It may be that after the distance between the control circuit of the mobile phone screen and the metal sheet is short, the capacitor increases, the impedance is reduced. The current can be discharged from other paths, and the circuit goes through. You can find a way to improve the impedance of this path or provide another low impedance path for the discharge current.
5. debug the LCD screen
1) The signal sequence, especially RS, is probably because the sent data is considered as a command and an error occurs.
2) the timing and duration of the reset signal. The reset signal is increased enough to send data.
3) initialize the order and correctness of commands.
4) Does the high-pressure opening during initialization meet the specification requirements?