The liquid crystal display module is a pure input component, or a passive component, for the whole system. The liquid crystal display module itself has no error correction function, that is, the liquid crystal display module can receive any signal that satisfies the operation sequence relationship without the ability to judge right or wrong, right and wrong. The wrong signal and the wrong data will produce the wrong control instructions or the wrong display pattern, resulting in the wrong display effect. The most important work to eliminate LCD electromagnetic interference is to find the source of interference and the location of interference, and then use effective methods to eliminate, weaken or shield and remedy.
1. The liquid crystal display module has no display, and the contrast adjustment has no response. This phenomenon is because during the operation of the whole machine, the power cord or signal line of the liquid crystal display module is subjected to electromagnetic interference, resulting in an interference pulse, resulting in the reset of the liquid crystal display module. The result of the reset is to initialize the internal register of the module and turn off the display at the same time.
2. The picture produces the wrong character or random point (data error), or the picture is translated, upside down and so on. Sometimes you can't recover, you can only clear the screen and rewrite, or even need to be powered up again before the initialization register can be restored. Most of this phenomenon is due to interference applied to control signals such as / WR signals, / RD signals, or E signals or / CS signals. The interference signal is easy to generate the wrong waveform on these signal lines, so that the register parameters are mistakenly modified, the display unit is mistakenly written to data, and so on. When the whole system is running, most programs only write data to the local display area, there is no write operation of other addresses, or some registers that are only set in initialization are not set repeatedly, so the above phenomenon occurs.
3. There is no source of interference, but there will also be no display or random display.
This situation is also classified as interference, but belongs to the interference within the system, mainly due to software program conflicts. The first consideration at this point is to interrupt the program. When the MPU is written to the liquid crystal display module (I addressing mode), the operation of the system is interrupted, and the control signal status of the liquid crystal display module or the data to be written may be modified. An error that causes the liquid crystal display module to panic or display content due to an error in the setting of the liquid crystal display module. The improved method is to turn off the interrupt response function when MPU calls the LCD drive subroutine.
4. No interference point can be found or circuit preventive measures can not be taken, but the effect of interference can not be eliminated.
At this point, you need to consider software remedies. The easiest way is to initialize the register at a fixed time. First of all, do not use the RESET signal to reset, only the register is duplicated. Because the reset action will cause the normal display to produce flicker, the display effect is not very good. If a crash occurs and cannot be recovered, the RESET signal can only be used to force the reset and then initialize the register.
5. The phenomenon of non-display or random display of liquid crystal display module caused by static electricity:
This is a common interference phenomenon, the interference pulse directly through the iron frame of the liquid crystal display module affects the circuit of the module. Usually the liquid crystal display module does not want the iron frame to float into an electrostatic charge storage surface, so it is connected to the VSS. However, this kind of connection can easily make the external interference directly affect the VSS line through the iron frame.
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