NB2DSK01 - TFT LCD Panel (with Touch Screen)

The NB2DSK01 provides high quality color display through a Hitachi TX09D50VM1CAA TFT (Thin Film Transistor) LCD panel. The panel also features an analog resistive touch screen.

Figure 1. TFT LCD panel with touch screen.

From a user perspective, you can either output straightforward graphics to the panel, or provide a more sophisticated level of interaction involving input to your FPGA design from the touch screen.

The NB2DSK01 motherboard utilizes the power of this display module to provide an interactive GUI with which to perform various board set-up functions – in essence a direct (and interactive) link with the firmware running within the NanoTalk Controller. For more information, see Interacting with the Desktop NanoBoard NB2DSK01.

LCD Display

The 3.5" panel features a Transmissive Color TFT LCD, with a resolution of 240(W) by 320(H). The display is based on an active matrix and backlight for the panel is provided through six LEDs.

Although capable of supporting 262144 colors (RGB, 6-bits parallel), the panel is fixed to use 16bpp display on the NB2DSK01, with bit 0 for both Red and Blue intensity inputs tied to GND. This results in a total of 65536 colors being available for display.

The panel requires various power supply levels. In addition to the on-board 3.3V level used for internal logic, a further three voltage levels are produced by the NB2DSK01 (using voltage step-up converter and regulator devices) based on the board's regulated 5V input. These levels are -7.5V, 9V and 16.5V, and are used for purposes including Gate and Source Driver power, contrast control and generation of Gray-scale voltage levels.

The panel connects to the NB2DSK01 motherboard through a 50-pin header. All display-based signals from I/O pins of the daughter board FPGA are routed through to this header, in addition to the required power supplies.

A 20K linear trimming potentiometer is used to provide contrast control, fed from the 9V power supply.

Figure 2. TFT LCD panel connection header and contrast control pot.

Touch Screen Control

Control for the TFT LCD panel's touch screen is provided through an AD7843ARU Touch Screen Digitizer (from Analog Devices). This device is essentially a programmable 8-/12-bit ADC. Powered by the NB2DSK01's 3.3V supply, it is capable of throughput rates of 125kSPS when clocked at 2MHz.

Figure 3. Touch Screen Digitizer.

Input to the Digitizer is the four-wire analog output from the touch screen, which relates to the position touched on the screen. The reference voltage used for the device is the same as the power supply, i.e. 3.3V. This determines the analog input range to the converter.

Communication between the daughter board FPGA/NanoTalk Controller and the Digitizer is performed over the SPI bus. From an FPGA design perspective, the following lists how the SPI interface signals from the daughter board FPGA are used:

• The SPI_SEL line selects the Digitizer for access. The serial input/output registers are enabled and the ADC conversion process is started upon this signal being received by the Digitizer (active Low).

• The SPI_DIN line is used to write to the Digitizer's control register.

• The SPI_DOUT line is used to transmit the converted data to the daughter board FPGA device.

• The SPI_CLK signal not only provides the clock source for the ADC conversion process, but also the serial clock for accessing the converted data.

The Digitizer provides an interrupt signal, wired to an I/O pin of the daughter board FPGA. This signal – DAU_TFT_IRQ – is sourced from the device's \PENIRQ output. This signal is kept normally High through use of an external pull-up resistance to the 3.3V power supply. When the touch screen is touched, the signal will be taken Low. The interrupt signal is used to alert a processor within the FPGA design that the panel has been touched. The embedded code running on the processor can then enter a routine to send a control word to the Digitizer, and hence initiate conversion.

Two further signals are provided by the daughter board FPGA:

• DAU_TFT_MUX – this signal is used to allow the daughter board to take 'control' of the TFT LCD panel. Tie this signal High so that your FPGA design has communication access to the panel.

• DAU_TFT_BLIGHT – this signal is used to control the TFT LCD panel's backlight, from within the FPGA design. Tie this signal High to keep the panel's backlight lit.

Location on Board

The TFT LCD panel comes already affixed to the right-hand side of the NB2DSK01 motherboard. The 50-pin header (designated LCD1), into which it is connected, is located on the component side of the board, to the right of the FPGA daughter board connectors.

The AD7843 device (designated U6) and 20K trim pot (designated VR1) are also located on the component side of the board, directly above and below the 50-pin header respectively.

The power-related circuitry for the TFT LCD panel, including voltage regulator (designated U9) and step-up DC/DC converter (designated U11), is located on the solder side of the board.

Figure 4. TFT LCD panel power circuitry.

Schematic Reference

The TFT LCD panel interface circuitry can be found on the following sheets of the motherboard schematics:

• Sheet 30 (TSC_AD7843.SchDoc, entitled TFT Touchscreen Interface)

• Sheet 31 (CON_LCD_TX09D50VM1CAA.SchDoc, entitled TFT LCD Header).

The additional power supplies generated for use by the TFT LCD panel can be found on the following sheets:

• Sheet 3 (PSU_BZX84C7V5_-7V5.SchDoc, entitled PSU BZX84C7V5 -7V5)

• Sheet 8 (PSU_LM317_9V0.SchDoc, entitled PSU LM317 9V0)

• Sheet 9 (PSU_LM2704_16V5.SchDoc, entitled PSU LM2704 16V5).

Design Interface Component

Table 1 summarizes the available design interface component that can be placed from the FPGA NB2DSK01 Port-Plugin.IntLib, to access and use the TFT LCD panel for purely graphical display purposes.

Should you wish to utilize the panel's touch screen, you will need to place the relevant design interface component that allows access to, and communications with, the Touch Screen Digitizer, as summarized in Table 2.

If your design involves communications with multiple SPI-based devices, you will need to place the generic SPI_BUS device. For more information, see Using Multiple SPI and I2C Devices in a Design.

Further Device Information

For more information on the TX09D50VM1CAA TFT LCD panel, refer to the datasheet (TX09D50VM1CAA[1].pdf) available at www.hitachi-displays-eu.com.

For more information on the AD7843 device, refer to the datasheet (AD7843.pdf) available at www.analog.com.