Chip Select, Data/Command, and Backlight pins:
Arduino D4 to TF_CS:
Used for SD card chip select (CS) SPI pin.
This pin will indicate the shield that the Arduino wants to send and receive data to and from the micro SD card.
Arduino D5 to TFT_CS:
Used for touch screen chip select (CS) SPI pin.
This pin will indicate the shield that the Arduino wants to send and receive data to and from the display/screen.
Arduino D6 to TFT_D/C:
Used for TFT Data/Command control pin.
The value of this pin (HIGH, or LOW) will tell the shield if the Arduino wants to send data or commands.
Arduino D7 to BACKLIGHT:
Used for touch screen backlight on/off control.
SPI Interface / Data Communication Pins:
Arduino D10 is SPI (CS) chip select pin:
This pin is not used by the TFT shield.
Arduino D11 is SPI (MOSI) data pin:
Used as data pin for SD card and screen. This pin is used by the Arduino to send data to the SD card or screen.
Arduino D12 is SPI (MISO) pin:
Used as data pin for SD card and screen. This is the pin that the Arduino uses to receive data from the SD card or screen.
Arduino D13 is SPI (SCK) pin:
Used as serial clock pin for SD card and screen. This pin is used to clock data in and out of the Arduino.