This article uses the MST717C display driver chip launched by MSTAR to drive the TFT liquid crystal display. As a vehicle multimedia information display terminal, it has the characteristics of low cost, good display effect and simple application. It focuses on the design of the MST717C peripheral circuit and the development based on MSTAR's Maria software architecture, which has a certain help for developers of TFT LCD displays. Follow WeChat Download Audiophile APP Follow the audiophile class related suggestion MST717C is a very cost-effective display driver chip with very few peripheral devices, which is very suitable for automotive display applications. ... NetLogic Microsystems, announced the launch of an innovative XLP8128S multi-core communications processor solution ... Atmel CorporaTIon, a leading manufacturer of touch and microcontroller solutions, announced that its 10.1 British ... SPMP8000 chip is a new handheld media processing chip launched by Generalplus Lingtong Technology Co., Ltd., using 2 ... The internal research report of the Ministry of Science and Technology: the polysilicon gap reached 20,000 tons in 2009. The Ministry of New Energy ... Polycrystalline silicon purification technologies include the Siemens method (including modified Siemens method), fluidized bed method and metallurgical method (including physical method). International production of high purity ... Enea releases OSE multi-core version of Enea (Nordic Exchange / Small Cap / ENEA) ...
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This article uses the MST717C series of chips developed by Taiwan's MSTAR company for small and medium-sized LCD screens, with video decoder (VIDEO Decoder) capability, supports a variety of analog video signal input, built-in zoom engine, built-in 51-MCU, 16-color OSD display And other functions, very suitable for vehicle multimedia display terminal applications.
1 Overall system design
MST717C supports NTSC, PAL, SECAM video signal input, built-in 2D comb filter, 2 CVBS input, 2 S-VIDEO input, support analog RGB input (such as analog VGA signal from PC). Supported video formats such as 480i, 480p, 576i, 576p, 720p, 1080i, analog RGB signal resolution support 640 × 480, 800 × 480, 800 × 60-0. Built-in brightness (Brightness), contrast (Contrast), saturation (SaturaTIon) and grayscale (Hue) adjustment, built-in 3-channel GAMMA curve adjustment, built-in zoom engine, can support up to 1366 × 768 resolution. Digital PWM controller, programmable control 40 ~ 70kHz frequency range data enable, horizontal synchronization signal output, 150 ~ 300Hz frequency range field synchronization signal output. Built-in 51-MCU, 3-wire serial bus interface, built-in hardware I2C, SPI, support 16 colors 256 programmable character OSD.
2 System hardware design
2. 1 MST717C peripheral circuit
Analog video signal input requires impedance matching to ground. Figure 2 shows the analog RGB input impedance matching circuit. The input signal is first isolated by a 120R magnetic bead to isolate high-frequency noise, and then 75 Ω impedance matching to ground and 35 Ω input impedance Match, place 47nF ceramic capacitive coupling input near the chip end. For CVBS, impedance matching to the ground and input impedance matching are also required. The typical value is 62Ω or 75Ω. The coupling capacitor can be a 0.1 μF ceramic capacitor.
2. 2 LED backlight driving circuit
Common TFT LCD panel module backlights are mainly divided into CCFL and LED. CCFL (Cold Cathode Fluorescent Lamp) technology is mature, low cost, and high brightness (luminance), usually above 400cd- / m2; the disadvantage is high-voltage AC drive (several hundred To thousands of volts), the driving circuit is complicated, the efficiency is low, and the heat generation is large. The main feature of LED backlight is low-voltage DC drive (tens of volts to tens of volts), simple driving circuit, high efficiency, and low heat generation; the disadvantages are high cost, low brightness, and poor color reproduction ability. At present, some large manufacturers of LCD modules have solved the problem of low backlight brightness by increasing the number of LEDs, and some can even reach 600cd / m2. In addition, the use of RGB ternary color LEDs to compensate for the color reproduction ability is better than the CCFL mode. Major manufacturers are optimistic about the LED backlight mode, which is also the main trend of LCD panel backlight development in the future.
Here we use the 8-inch widescreen LCD module A1080TN03 developed by Innolux, with a physical resolution of 800 × 480, 260,000 colors, LED backlight, a typical driving voltage of 10V, and a driving current of 100-200mA. The backlight power input is 5V, and the DC-DC boost chip KB4317 is used to stabilize the output at 10V.
2. 3 audio signal processing and amplifying circuit
PT2314 is a low-cost and high-performance four-input digital audio processing chip developed by Taiwan Pucheng Technology. It supports volume, left and right channel balance, high and low sound (Treble & Bass), loudness (Loudness), etc. Selectable input gain (Selectable input gain), support standard I2C interface. The PT2314 control port I2C is connected to the MST717C software analog I2C interface. It should be noted that the I2C transmission line needs to be pulled up to ensure the reliability of the transmission.
3 System software design
3.1 The overall framework of Maria software
Maria is the public version of the driver software source code launched by MSTAR for the MST71X series of chip applications. The source code is mainly based on the KEIL C51 language, but due to its relatively complex and large amount of source code (tens of thousands of lines), it is for ordinary users. Come some difficulties. The style of Maria source code is somewhat similar to the style of linux kernel source code, mainly including Device, inc, kernel, msFunc, msLib, osd, project, tv and other folders.
Under the Device folder is the driver code of the user's specific device. Here we will add the driver code of PT2314 and put it in a name named PT2314. In the file of C, it is mainly to initialize the PT2314 chip and give some interface functions of the sound operation class.
Inc folder is mainly some header files, including the application of global variables Global. h, font header file Font. h, based on the 51 core microcontroller header file mcu. h, and header files for parameter definitions of various screens.
The Kernel file mainly contains the main function main. c. mcu initializes mcu. c. Global variable initialization to achieve Global. c. The interrupt service function implements isr.c, and the debug help function implements Debug. c. MST7lX series chip register configuration function mStar. c and some commonly used functions misc. c etc.
Under the msFunc file, it is mainly the realization of some functional operation functions, such as the Keypad. c. Infrared remote control IR. c. IRFunc. c. OSD menu class msOSD. c. Game. c. Menu function category MenuFunc. c etc.
Under the msLib file are some dynamic library files about the DSP processor, which are hidden from the developer and users can ignore these files.
The Osd file contains some font and picture files. The user can add the desired text (such as Chinese characters) and binary icons to the corresponding file after taking the mold through the mold taking software.
The Project file is mainly about KEIL C engineering files, which are divided into 64k and 128k. Generally, it is better to choose 128k.
Tv is some operation functions written by MSTAR specifically for analog TV users.
3.2 The concrete realization of each function
3.2.1 Sound effect processing chip driver
This system mainly expands the sound processing chip PT2314 around the MST717C. The PT2314 supports the standard I2C protocol. It shares the MST717C GPl00 and GPI01 software with 24LC16 to simulate I2C. The MST717C hardware I2C is used as the chip program programming function.
3.2.2 OSD menu customization
Maria provides a standard OSD menu frame, which mainly includes color, contrast, brightness, screen display area adjustment, timing shutdown and so on. The Maria OSD menu contains three levels of menus, the first level of the root directory root; the second level of menu contains 5 directories including images, volume, functions, system, and time; the third level of directory is the internal menu items of each second level directory, such as the image menu Contains four three-level menus of brightness, chroma, contrast, language and so on. Users can add and delete any level menus. The PT2314 sound processing chip is selected in this system. It supports four-channel stereo input. The host can control the volume, bass, treble, balance and other options through the I2C bus. Create three levels of volume (Volume), bass (Bass), treble (Treble), and balance (Balance). MenuTbl. Create the corresponding menu array MenuItemTypecode AudioMenuItems [] = {) in the h file: where MenuItem-Type is a data structure whose prototype is
Contains the relative position of the menu item, background color, color when selected, associated lower level menu, menu drawing type, display text, key corresponding event, function, display type, logo, etc. The meanings can basically be understood by the text description. It should be noted that the MST717C OSD menu only supports 16-color display. Here is a sub-menu of PT2314 as an example,
3.2.3 Key event
The user keys are sampled differently by ADC key values. When different keys are pressed, the ADC gets different voltage values ​​(see Figure 4). The main loop of the program continually executes the key scan function Key ScanKeypad () to query whether a key has been pressed. If a key is pressed, the program first compares it with the last key value (g ucLastKeypad). If they are equal, the repeated key event EventRepeatProcess () is executed; if they are different, the key event EventProcess () is executed, and the key is pressed. The value is set to g ucLastKeypad.
Maria key event is mainly completed by a data structure defined as KeyEventType type. The first element in the data structure is the key input state. There are two input states, INPUT PRESS and INPUT_HOLD, where INPUT_PRESS is the key pressed state, which only represents the state when it is pressed; INPUT_HOLD is the continuous state when the key is pressed, which is equivalent For quick combos. The second element is the event that will be executed when the button is pressed, and its data structure is MenuItemAcTIonType. Note that the Menultem-AcTIonType events corresponding to the same key in different KeyEventType events are also different, in order to distinguish the different functions performed by the same key in each level of directory. The last element is the input type InputPortType, which is an enumerated variable, which represents the key input of different video source states. For example, the Power key input corresponds to Input_AllPort, that is, the key is valid in any state; and the remote control key 1 input is 1 <
4 Conclusion
MST717C is a very cost-effective display driver chip with very few peripheral devices, which is very suitable for automotive display applications. It should be noted that the display driver has relatively high requirements on power supply stability. It is best to split the analog ground and the digital ground during PCBLayout to ensure the stability of the video signal. If the cost allows, it is best to choose a four-layer board. Water ripples are easy to occur if the power supply is not handled well. In addition, the VCOM voltage must be stable to ensure the stability of the displayed image. In addition, the Maria software architecture is a bit complicated, and the C language requirements for developers are somewhat high. It takes a certain amount of time to read its code and then conduct its own secondary development.
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