Unlike most FeatherWings, the TFT FeatherWing is fully assembled and has a dual socket set for your Feather to plug into.
This makes it really easy to use, but a little different to change if you don't want the default setup
The 3.5" TFT FeatherWing has a really beefy backlight, and we don't want to overwhem the 3.3V regulator on the Feather so we use two Schottkey diodes to take the higher of VBAT and VUSB to feed into the backlight boost converter.
The GND and 3.3V pins are used for powering the rest of the device such as the TFT and touchscreen controller
You can turn off the 3.3V power supply with the EN pin or the switch attached to that pin. The enable/disable switch on the bottom of the Wing will also deactivate the backlight
Note that on the Teensy 3x Feather Adapter, this pin doesn't do anything and on the FONA feather, this will not disable the VBAT power supply which is used to power the cellular module.
The TFT display, SD card and touch screen use the SPI interface to communicate. That means MISO, MOSI and SCK are used whenever either are accessed.
(Ooops the highlighted pins are off by one, they should be shifted to the right one pin!)
In addition, for the TFT display there is are DC (Data/Command) and CS (Chip Select) pins. These are used to select the display and tell it what kind of data is being sent. By default, DC is connected to pin 10 and CS is connected to pin 9. These pins can theoretically be changed by cutting the jumper trace and soldering a small wire from the farther-from-the-socket-header pad to the pin you'd like to use.
On the ESP8266, TFT_CS is pin #0, TFT_DC is pin #15
On the ESP32, TFT_CS is pin #15, TFT_DC is pin #33
On the Atmega32u4, ATmega328p, M4 or M0 Feather, TFT_CS is pin #9, TFT_DC is pin #10
On the Teensy Feather, TFT_CS is pin #4, TFT_DC is pin #10
On the WICED Feather, TFT_CS is PA15 and TFT_DC is PB4
On the nRF52 Feather, TFT_CS is #31 and TFT_DC is #11
There is also LITE pin which is not connected to any pads but you can use to control the backlight. Pull low to turn off the backlight. You can connect it to a PWM output pin.
The touch screen also has a Chip Select line, labeled RT. By default RT is connected to pin 6. This pin can theoretically be changed by cutting the jumper trance and soldering a small wire from the right-hand pad to the pin you'd like to use.
On the ESP8266, RT is pin #16
On the ESP32, RT is pin #32
On the Atmega32u4, ATmega328p, M4 or M0 Feather, RT is pin #6
On the Teensy Feather, RT is pin #3
On the WICED Feather, RT is PC7
On the nRF52 Feather, RT is #30
There is also an IRQ pin which is not connected to any pads but you can use to detect when touch events have occured.
The SD Card also has a Chip Select line, labeled SD. By default, it is connected to pin 5. This pin can theoretically be changed by cutting the jumper trance and soldering a small wire from the right-hand pad to the pin you'd like to use.
On the ESP8266, SD is pin #2
On the ESP32 SD is pin #14
On the Atmega32u4, ATmega328p, M4 or M0 Feather, SD is pin #5
On the Teensy Feather, SD is pin #8
On the WICED Feather, SD is PC5
On the nRF52 Feather, SD is pin #27