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ILI9341 LCD TFT Readme

Image TFT

Table of contents

Overview

  • Name: ILI9341_TFT
  • Description:
  1. C++ Library for a TFT SPI LCD, ILI9341 Driver (might also work with ILI9340)
  2. Dynamic install-able or Linux Single Board Computers C++ library.
  3. Inverse colour, rotate, scroll, modes supported.
  4. Graphics + print class included.
  5. 24 bit colour , 16 bit color & bi-color Bitmaps supported.
  6. Hardware and Software SPI
  7. Dependency: lgpio Library
  8. Support for XPT2046 Touchscreen IC included
  9. NB 'spidev.bufsiz' setting must be 65536 or greater see Notes section.
  • Author: Gavin Lyons

Software

User options

In the example files. There are 3 sections in "Setup()" function where user can make adjustments to select for SPI type used, and screen size.

  1. USER OPTION 1 GPIO/SPI TYPE
  2. USER OPTION 2 SCREEN SECTION
  3. USER OPTION 3 SPI SETINGS

USER OPTION 1 SPI TYPE / GPIO

This library supports both Hardware SPI and software SPI. The TFTSetupGPIO function is overloaded(2 off one for HW SPI the other for SW SPI). The parameters set for TFTSetupGPIO define which is used.

USER OPTION 2 Screen size

User can adjust screen pixel height, screen pixel width The function TFTInitScreenSize sets them.

USER OPTION 3 SPI Settings

TFTInitSPI function is overloaded(2 off, one for HW SPI the other for SW SPI).

parameter default value note SPi type
HWSPI_DEVICE 0 A SPI device, >= 0. which SPI interface to use , ls /dev/spi* Hardware
HWSPI_CHANNEL 0 A SPI channel, >= 0. Which Chip enable pin to use usually 0 or 1 Hardware
HWSPI_SPEED 1000000 The speed of serial communication in bits per second. Hardware
HWSPI_FLAGS 0 mode 0 for this device Hardware
GPIO_CHIP_DEVICE 0 gpio chip device >= 0, check ls/dev/gpiochip* both
SWSPI_CommDelay 0 uS delay for GPIO software

The user can adjust if having reliability issues with SW SPI in some setups. This is a microsecond delay in SW SPI GPIO loop. It is set to 0 by default, Increasing it will slow down SW SPI further.

File system

In example folder: The Main.cpp file contains tests showing library functions. A bitmap data file contains data for bi-color bitmaps and icons tests. The color bitmaps used in testing are in bitmap folder, 3 16-bit and 5 24-bit images.

# example file name Desc
1 Hello_world Basic use case
2 Text_Graphic_Functions Tests text,graphics & function testing
3 Bitmap_Tests bitmap + FPS testing
4 Mandelbrot_set Drawing a mandelbrot set demo
5 Touch_Screen Basic Touch screen demo
6 xpt_Test Touch screen test without TFT
7 Hello_world_SWSPI Basic use case software SPI

Hardware

Tested and developed on:

  • Size 2.4 inch SPI Serial IPS color TFT LCD
  • Resolution: 240 (H) RGB x 320 (V)
  • Color Depth: 262K/65K (65K used)
  • Control chip:ILI9341
  • Display area 27.972 (H) x 32.634 (V)
  • Panel size 36.72(W)X48.96(H)mm
  • Logic voltage 3.3V
  • Touch panel with XPT2046 IC

Connections as setup in main.cpp test file.

PinNum Pin description RPI note
1 VCC VCC 3.3 or 5V ,CAUTION your display must have 3.3V regulator on back to connect to 5V
2 GND GND
3 CS SPICE0 TFT Chip select
4 RESET GPIO25 Reset, Use any GPIO for this, If no reset pin, pass -1 in here & display will use software rst
5 DC GPIO24 Data or command, Use any GPIO for this line
6 SDI(MOSI) SPIMOSI
7 SCLK SPICLK
8 LED VCC CAUTION Your display may need current limit resistor
9 SDO(MISO) nc Only needed to read diagnostics from TFT (not implemented yet)
10 T_CLK SPICLK
11 T_CS SPICE1 XPT2046 Chip select
12 T_DIN SPIMOSI
13 T_DO SPIMISO
14 T_IRQ GPIO22
  1. This is a 3.3V logic device do NOT connect the I/O logic lines to 5V logic device.
  2. LED Backlight control is left to user.
  3. Pins marked with T_ prefix are related to the touchscreen IC XP2046 if user is not using the touch screen do not connect these. The touch screen and TFT share the SPI bus but have different chip select lines. TFT SPI settings(Speed, active chip select) should be refreshed after ever read cycle of XPT2046 sensor, see example.

Output

Four-Byte Burger 240x320 16-bit bitmap test image, Credits Ahoy

output pic

Touchscreen

If the users display has a touchscreen controller IC on the back (XPT2046). A simple class to interface with the XPT2046 touchscreen controller IC has been included. Note :It may not be populated on your display or there may be a different model of IC there.

The T_IRQ line goes low when the touchscreen is touched and the data can be read from sensor.

Co-ord system returned by XPT_2046_RDL class is as follows:

  1. Top left : X = 1800 Y = 150
  2. Top Right : X = 150 Y = 150
  3. Bottom Left : X = 1800 Y = 1800
  4. Bottom Right : X = 150 Y = 1800

Output of the basic touch screen example included.

output pic

Notes

spidev buf size

The maximum transaction size that 'lgpio' can handle by default is 65536 bytes. So this is also the maximum transaction size of Display_lib_RPI, if more than that needs to be sent it is sent in blocks of 65536 bytes. Certain 'Display_lib_RPI' functions use buffered writes, the ones that draw bitmaps, write fonts, fill rectangles, clear screen, etc. In order for this to work the spidev.buf size must be at least 65536. To check the setting on your device run command:

cat /sys/module/spidev/parameters/bufsiz

If it is lower than 65536 you can change it by adding this to the start of line in file /boot/firmware/cmdline.txt.(raspberry pi ) Make sure everything is on one line and there is space ' ' between this parameter and next one. Then reboot machine. Verify again by running last cat command above

spidev.bufsiz=65536

bufsiz defines the number of bytes that the SPI driver will use as a buffer for data transfers.