PDA LCD design
2011-11-13 by seoer1

Abstract: A microprocessor-based Pocket PC SA1110 LCD controller, interface, display principle-driven approach was introduced. HPC is engaged with the project, proposed a microprocessor-based Pocket PC SA1110 LCD design.

Keywords: SA1110 microprocessor Pocket PC (HPC) liquid crystal display (LCD) touch screen (TP)

Along with the network represented by the new economic era, PC has lost its former luster, intelligence 3C products (Computer, Communication and Consumer) will trigger a new wave of waves. Pocket PC smart 3C as a representative of the product, its transmission quickly, convenient, versatile features, is becoming a mainstream product by consumers.

At present, the more popular Pocket PC CPU family are MIPS, SuperH series, DragonBall series and ARM series. In the field of operating systems, in addition to some of the Linux operating system and self-development, the majority of products using Palm OS, Windows CE and EPOC operating system.

Pocket PC to the embedded system in major application areas once occupied the land, Tsinghua University and Shenzhen Grand auto company decided to develop a national intellectual property rights Pocket PC. This requires selecting and developing their own hardware platform; but also develop their own embedded Linux operating system; in the hardware platform and operating system, and then develop specific applications to meet specific user needs. This article describes the design of the LCD display is the important part of system design.

A hardware circuit

PDA-based SA1110 LCD microprocessors mainly consists of three parts: LCD controller, CPLD and ASIC chip liquid crystal display LCD.

2 SA1110 LCD controller

The chip integrates SA1110 LCD controller, the controller has three display types:

· Passive color mode: 3375 kinds of color, each frame allows the display of 256 colors;

· Active color mode: supports up to 65,536 kinds of color (16 bit);

· Passive monochrome mode: support 15 levels of gray.

LCD controller supports up to 1024 × 1024 pixel display screen. However, in the frame memory, because memory bus width, pixel size limit of the encoded data to drive the LCD display screen size. LCD controller also supports single-and dual-screen display. Pixel encoded data stored in external memory, LCD dual-channel DMA controller according to the specific circumstances of the data into a 5-unit (32-bit length) of the queue buffer. A channel DMA controller for single-screen display, one for dual display.

In the frame memory, stores pixel encoded data. LCD controller to be used as a pointer to index a 256-unit 12-bit wide color palette. 4-bit wide black and white palette, color palette 12-bit wide. Pixel from the frame memory encoding data (4) addressing the top 16 black and white palette unit; 8-bit pixel data can be encoded in the palette to access any of 256 units. 12 pixels in passive mode, color, color pixel data is bypassed directly to the LCD color palette and jitter logic. 16-bit pixel color in the active mode, the color pixel data is not only pass out color palette, and pass out the LCD jitter logic, and data directly to the LCD pins. Once the 4 or 8-bit pixel data coding unit selected a color palette, this unit is encoded in the value of jitter transferred to the logic circuit. Jitter logic circuits using a space-based and time-based algorithm to generate the output to the screen's pixel data. Jitter logic which each and every pixel at different rates in each frame on the off, so to produce 15-level grayscale monochrome screen, color screen for the red, green and blue color in each of which produces 15 color degrees, a total of 3375 kinds of color (256 colors available for each frame). Jitter from the logic circuit output data is output to the LCD pixel clock pin and drive the display before being placed in a 9-pin data unit queue buffer.

Depending on the type of display, LCD controller can be programmed for 4, 8-bit or 16-bit pixel data pins. Single-screen monochrome monitor each pixel clock cycle both in the use of four 8-bit can also be used to output data pin 4 or 8-bit pixels. Single-screen color display can be used to pin 8-bit data per pixel clock cycle to output 2 to 2 / 3 of the pixel (8-pin / 3 color / per pixel). LCD controller also supports dual display. Dual-display LCD controller data lines are led into two groups, one group of drivers on the half-screen, half screen, driven by the other group.

In this scenario, passive color mode is selected. CPLD PZ3128 is Philips's ASIC. As the handheld device's LCD display a wide range of manufacturers to make the standard consistent with the SHARP SA1110 LCD controller's 3.9-inch TFT Active Color LCD display in the data format and timing can not match. Therefore, the CPLD PZ3128 can be programmed for different data formats data mapping interface for the configuration of different types of LCD screens dedicated ASIC chip.

SA1110 LCD controller consists of the following pins:

· LDD [0 ~ 7]: 7-bit data line, for 4 and 8-bit display mode, but also 16-bit TFT mode the lower 8 bits;

· GPIO [2 ~ 9]: When using the LCD module is 16-bit TFT mode, constitute the high 8-bit data line;

· L_PCLK: Pixel Clock (Pixel clock), for each point of data into the shift register;

· L_LCLK: Line clock (Line clock), is used to indicate a line of data from the shift register to the display driver chip transmission is completed, and makes the line pointer. In the 16-bit TFT mode is horizontal sync signal;

· L_FCLK: Frame Clock (Frame clock), used to indicate the start of an image, while the line pointer in the first line of the display. In the 16-bit TFT mode is the vertical sync signal;

· L_BIAS: 16-bit TFT mode, the output enable signal, the data signal used to indicate the synchronization of the clock signal, the latch to the pin.

In order to show an image, SA1110 LCD controller first open a buffer in RAM as a frame buffer (FRAME BUFFER). Stored image data to be displayed, and then let the LCD modules controller's DMA address register points to FRAME BUFFER starting address, read out the FRAME BUFFER data to the input FIFO queue (INPUT FIFO). As used in this design 16-bit mode, the frame buffer without decoding the data, so the LCD controller does not process the data directly to the output FIFO queue (OUTPUT FIFO). OUTPUT FIFO data is then sent through the CPLD pins to drive the liquid crystal display. As SA1110 LCD controller has its own independent dual-channel DMA, while selection of high-performance SDRAM, to meet the display bandwidth.

3 LCD Module

As prices fall, liquid crystal display due to low power consumption, no radiation, light is widely used in various handheld devices. Especially the TFT-LCD, high resolution, wide viewing angle, high contrast, etc., in the high-end handheld computer used more often.

As the SA1110 SOC chip with LCD controller in itself, support 8, 12 and 16-bit format many types of monochrome and color LCD, the developer's choice to bring great convenience. According to the user's requirements, taking into account the actual display, the program chose SHARP 3.9 inch TFT color LCD active type, the specific model: LQ039Q2DS54. The display module is a color reflective and active-matrix LCD modules, TFT color LCD screen from the driver IC, FPC lead, front lights, touch screen, and after the closure panels. Lattice in the form of 320 × 3 × 240, can display graphics and text, can display up to 262,144 kinds of colors.

LCD module requires 10 levels of standard analog pulse voltage V0 ~ V9, for LCD grayscale display module internally generated reference. These voltage direct impact on the LCD display of color and grayscale accuracy, high precision requirements of its value. At the same time, they are the pulse signal, the edge of steep requirements to ensure the display point clear. V0 ~ V9 amplitude parameters required are shown in Table 1.

Table 1, the first voltage signal arrays with high precision resistors, resistor divider which generates the reference voltage, then a second election in accordance with LCD display frame switching frequency of high-speed switching, the output can get the standard analog pulse voltage. Among them, a second election switch selection LMC6009.

Table 1 V0 ~ V9 amplitude parameters

Pulse amplitude V1 V2 V3 V4 V5 V6 V7 V8 V9 V0
VA (V) 3.30 3.10 2.60 2.35 2.10 1.90 1.60 1.15 0.50 0.10
VB (V) 0.60 0.90 1.45 1.75 2.00 2.30 2.60 3.30 3.60 3.90

LQ039Q2DS54 with many of the TFT, as each pixel 18-bit encoding. Red, green, blue color 6 each, that is RGB666. But the SA1110 LCD controller supports 16-bit mode, it must be red, blue the lowest ground, creating 5 red, 6 green, 5 blue The RGB565 format. This produces a color difference is very small.

4 Touch Screen

Typically, for the touch screen handheld devices are generally installed with the integrated LCD screen together, close to the surface of the LCD. SHARP 3.9 inch T6963C Graphic LCD module (LQ039Q2DS54) surface with a resistive touch screen.

Through the resistive touch screen, can measure the position and contact pressure. When testing the X coordinate, the first ends of the plate to the X bias voltage, then test tspy, tsmy one or all. They are equivalent to the potentiometer's wiper, the measured voltage is proportional to the contact of the X coordinate. Similarly, Y coordinates of the test, just the X and Y plate interchangeable plate only. SHARP 3.9 inch TFT LCD (LQ039Q2DS54) surface mount resistive touch screen parameters are as follows:

· Input voltage: 5V;

· X1 and X2 between the resistance: 320Ω;

· Y1 and Y2 between the resistance: 580Ω;

· X or Y direction of the line of linearity: 1.5%;

· Insulation resistance greater than: 20MΩ;

· The minimum detectable pressure: 24g.

The design used in the Philips company UCB1300 not make as MODEM and audio analog front-end chip, and its integrated touch screen controller, can be more than one use, easy to use the handheld system. Touch screen controller features include: the touch screen bias voltage is applied between two plates, when clicks, an interrupt signal; while clicking the X and Y directions at the analog voltage signal for digital quantification, has been the position is data stored in the internal register; interface to read through the MCP microprocessor. UCB1300 associated with the touch screen controller features include:

(1) full four-wire resistive (pressure sensitive) touch screen interface circuit are connected to the four touch-screen signal line tspx, lsmx, tspy and tsmy, can achieve position, pressure and plate resistance measurements.

(2) with an internal track and hold circuit and analog multiplexer 10-bit successive approximation ADC, the data used for touch screen readout and contacts outside the circuit 4 analog voltage monitor, which the external circuit with four analog voltage monitor for power management.

(3) with internal reference voltage source, and provide the basis for the 10-bit ADC reference voltage and the virtual ground. This can be exempted from the supply voltage and temperature variations.

(4) 4-wire high-speed serial interface data bus, with the main processor to achieve the MCP SA1110 synchronous serial communication, a strict definition of the data frame.

(5) touch screen different modes of internal control by the UCB1300 register set, and these control registers by the SA1110 synchronous serial port to read and write by MCP.

(6) because the LCD touch screen with nearly coupling, the large LCD screen from interfering signals may affect the peak of the touch screen work, so the touch screen controller with four internal low-pass filter to reduce high frequency interference from the LCD .

Although the domestic market, a variety of PDA and handheld computers are more, some domestic brands are also very popular, but in product design and manufacturing, Taiwan and other manufacturers are relying on the OEM, research and development of truly autonomous hardware platform almost zero. Therefore, the Pocket PC hardware platform project successfully developed the system, in particular, is based on the Intel StrongARM SA1110 CPU high-performance prototype, still in the leading position in the country, and for the same group developed a variety of embedded operating systems and applications that provide hardware environment.

  keywords:t6963c graphic lcd module