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A MOSFET turns the backlight LEDs on/off and a 4.7ohm resistor limits the maximum current through the LEDs. This makes it quite easy to control the backlight with a PWM signal to adjust intensity. 8297A-AVR-04/10 The SPI interface The Display Xplained module uses a simple SPI interface to communicate with the LCD module. This consist of a Chip-Select (CS) line, a clock line (SCL), and two data lines (SDI/SDO). The SPI is operated in mode 3, i.e. inactive clock is ‘high’, and data is latched on rising clock edge. 3.5 The SPI/USART MUX resistors The ATxmega128A1 has swapped the MOSI and SCK signals between using the regular SPI and using the USART in master SPI mode, which is available on the same pins. In order to offer the possibility to use both interfaces, a simple 0-ohm resistor mux is added to the Display Xplained module. It is currently set up to use the USART in master SPI mode. To switch to the regular SPI mode, move the two resistors mounted in position R111/R114 to position R112/R113. See schematic diagram and PCB assembly drawing for details on where to find these resistors. Note that they are placed under the LCD flexprint cable, so this needs to be disconnected from the FPC connector to get access to the resistors Please refer to Figure 2-1 page 2. 3.6 The LCD Tear-Enable signal (TE) The LCD Module has an output signal that indicates when the display can be updated without getting any tearing effects. This signal basically indicates the scan retrace period of the display, meaning the time-period after the last pixel update and before the first pixel is written again. This period can be used to update the graphical RAM, and the update will be shown in the next scan period. For further details, see the Himax HX8347-A datasheet and application notes. 3.7 The LCD Reset signal This signal is an input to the LCD module and is used to reset it. It has a pull-up resistor connected to avoid unintended resets. For further details, see the Himax HX8347-A datasheet and application notes. 4 Connectors The Display Xplained module has five 10-pin 100mil headers. Two are used for programming/debugging interface to the Xplain kit. One is used for SPI interface and the backlight control of the LCD module. One is used for the touch interface to the LCD module. The last one is only used as a mechanical stabilizer to the Xplain kit. Note that the female SMD mounted pin-headers might get damaged if not handled carefully. The plastic insulation might come off and exposes the conductors. The last connector on the Display Xplained module is the FPC connector for the LCD module. 4.1 Programming headers (J103/J104) The AVR XMEGA™ can be programmed and debugged by connecting an external programming/debugging tool to the “JTAG & PDI XMEGA” pin header (J100). The pin header is having a standard JTAG programmer pinout (refer to online help in AVR Studio®), and tools like the JTAGICE mkII or the AVR ONE! can thus be connected AVR1909 8297A-AVR-04/10 AVR1909 AVR1909 or squid cable (included in the JTAGICE mkII kit) must be used. Please see Table 4-1 below for pin-out description. Table 4-1. Programming headers (J103/J104) – JTAG and PDI. J103/J104 pin JTAG(1) PDI(2) J103/J104-1 TCK - J103/J104-2 GND GND(3) J103/J104-3 TDO - J103/J104-4 V3P3 V3P3(3) J103/J104-5 TMS - J103/J104-6 nSRST PDI_CLK J103/J104-7 V3P3 V3P3(3) J103/J104-8 -PDI_DATA J103/J104-9 TDI - J103/J104-10 GND GND(3) Notes: 1. Standard pin-out for JTAGICE mkII and other Atmel programming tools. 2. Requires adapter or squid cable to connect a JTAGICE mkII (refer to AVR Studio help). 3. It is only required to connect one V3P3/GND pin. The AT90USB1287 can be programmed by connecting a programming tool, such as a JTAGICE mkII, to the “JTAG USB” pin header (J200) on the Xplain board. Please refer to AVR1907: Xplain Hardware User’s Guide for details. 4.2 The resistive touch pin-header (J101) This connector connects the resistive touch interface to AVR XMEGA’s analog PORTA that is available on the “XMEGA PORT A” pin header on the Xplain board (J101). This allows the user to connect external signals to the ADC, DAC and Analog Comparators on PORTA. Please see Table 4-2 below for pin-out description Table 4-2. The resistive touch pin-header (J101) connections. J101 pin LCD resistive touch signals J101-1 - J101-2 - J101-3 - J101-4 - J101-5 TFT_XL (X-direction, Left side) J101-6 TFT_XR (X-direction, Right side) J101-7 TFT_YD (Y-direction, Bottom [lower] side J101-8 TFT_YU (Y-direction, Upper side) J101-9 GND J101-10 - 8297A-AVR-04/10 The SPI/TE/Reset/backlight pin-heade...

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