Overview of LCM

Debugging an LCM, or screen adjustment, is one of the most basic tasks we do for the driver.

LCM is a module that is usually packaged by the screen factory. It generally consists of several parts:

1. The glass. The part of the display image that we see is the most important device in LCM. It contains liquid crystals, electrodes and so on.

2. IC. That's what we call a display chip. It's the device that controls the glass to display the image, and what we're doing is we're actually making the display chip work with our BB.

3. Peripheral devices. Including PCB board, capacitor resistance on PCB board, backlight, etc.

Notes before changing the screen

We usually need to do some preparatory work before we actually adjust the screen, which will help us to avoid detours in future screen adjustments. First look at the schematic diagram to confirm whether the signal control line of the screen is connected correctly. See that the data line is connected to several bits. The data transmission mode of 8-bit, 16-bit and 18-bit is different, which is controlled by different macros in the program. Take a look at the SPEC of IC and see how the registers are set; Registers control the distribution of various functions, such as control voltage, control position, control effect, and so on; And to see if its timing fits our BB.

The frequency of the PWM

For LCD backlight, the general practice is to boost the chip to provide voltage support. And these booster chips will have PWM input PIN, through PWM to adjust the Brightness and darkness of the backlight. However, sometimes we will find that the adjustment amplitude of backlight suddenly increases and decreases, or the backlight is not bright enough (relative to GPIO PIN output HIGH). However, when measuring PWM input via multimeter, the voltage drop amplitude is in normal condition. At this time, we might as well reduce THE OUTPUT frequency of PWM. Since many booster chips require PWM frequency, tuning the frequency to the range indicated in the datasheet can generally solve this problem.