Interface ILI9341 based TFT display with T4.0

Lavanya rajan · Jun 24, 2025

Hello All,

I'm trying to interface a 2.4" TFT SPI 240x320 display with a Teensy 4.0 microcontroller. The pin connections follow the setup described in the link below, except that the CS (Chip Select) pin is connected to pin 9, and the DC (Data/Command) pin is connected to pin 10.

PJRC Store

www.pjrc.com

I'm using the following code, but the text on the display appears mirrored, even though the rotation is set correctly and also The background color isn't displaying properly — I'm using fillScreen(RED), but the screen shows blue instead.. Can anyone help me figure out what's causing this and how to fix it?

Code:

#include <SPI.h>
#include <Wire.h>
#include <ILI9341_t3.h>

// Define pins for the TFT display
#define TFT_CS 9
#define TFT_DC  10

ILI9341_t3 tft = ILI9341_t3(TFT_CS, TFT_DC);

void setup(void) {
  Serial.begin(9600);
  tft.begin();

  // Try different values (0 to 3) if needed: 0 = portrait, 1 = landscape, 2 = upside down, 3 = other landscape
 
  tft.setRotation(1); // Usually best for non-mirrored portrait
  tft.fillScreen(ILI9341_RED); // Set background to blue

  // Optional: disable text wrapping
  tft.setTextWrap(false);

  // Set text properties
  tft.setTextColor(ILI9341_WHITE); // Text color
  tft.setTextSize(2);              // Text size
  tft.setCursor(30, 30);           // Adjust position

  // Display the message
  tft.println("Hello World!!!");
}

void loop() {
  // Nothing to do here
}

defragster · Jun 24, 2025

what version of teensyduino and what IDE are in use?

Try one of the examples included with the library just to be sure the behavior persists.

Lavanya rajan · Jun 24, 2025

defragster said:
what version of teensyduino and what IDE are in use?

Try one of the examples included with the library just to be sure the behavior persists.

Version: 2.3.4
Date: 2024-12-03T10:03:03.490Z
CLI Version: 1.1.1

Copyright © 2025 Arduino SA

Teensyduino version is 1.59.0

defragster · Jun 24, 2025

Lavanya rajan said:
Version: 2.3.4

Some use non Arduino and that can be an issue.

Any luck with seeing similar using one of the provided library examples and the inverted text?

Lavanya rajan · Jun 24, 2025

defragster said:
Some use non Arduino and that can be an issue.

Any luck with seeing similar using one of the provided library examples and the inverted text?

I'm using examples codes from this link https://github.com/vindar/tgx which contains programs related to T4.0, I uploaded few examples and all these are appearing inverted

defragster · Jun 24, 2025

I'd close the IDE and restart using one of the examples like:

"T...\hardware\teensy\avr\libraries\ILI9341_t3\examples\graphicstest\graphicstest.ino"

There may be a badly compiled file in the TEMP build folder.

Also with Verbose build at the end the actual library in use is noted and it should link to the one in the TeensyFolder and not a local library copy - something like this (as shown using path for IDE 1) - there is will come from the USER APPDATA LOCAL folder (windows?) but the BOLD TAIL shown and version should be similar:

Using library ILI9341_t3 at version 1.0 in folder: T:\T_Drive\arduino-1.8.19\hardware\teensy\avr\libraries\ILI9341_t3

Lavanya rajan · Jun 24, 2025

So, this is the location where all files are saved C:\Users\SMDDC2\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\libraries\ILI9341_t3\examples\graphicstest

I uploaded the graphicstest.ino available in the above path, again everything is displayed in inverted

defragster · Jun 25, 2025

Something odd about the display there it seems. Not the same or using the same actual interface chip.

AFAIK this hasn't shown up in the years this display has been in use.
Is only a single copy of this display there to test?
Compare the visible markings on the PJRC page - and maybe upload a phonto of the backside not showing on that page.

Lavanya rajan · Jun 25, 2025

defragster said:
Something odd about the display there it seems. Not the same or using the same actual interface chip.

AFAIK this hasn't shown up in the years this display has been in use.
Is only a single copy of this display there to test?
Compare the visible markings on the PJRC page - and maybe upload a phonto of the backside not showing on that page.

I already uploaded backside of the display in the top

defragster · Jun 25, 2025

Lavanya rajan said:
already uploaded backside of the display in the top

indeed

That is 2.4" - the handy ones here are not 2.4" so not clear that may not have a different controller that ILI9341. SImple variations can show big differences.

PJRC suggests 2.8" or 3.2" were the common sizes used when ILI9341 code was tested

Lavanya rajan · Jun 25, 2025

Any input on how to sort out this issue

defragster said:
indeed
That is 2.4" - the handy ones here are not 2.4" so not clear that may not have a different controller that ILI9341. SImple variations can show big differences.

PJRC suggests 2.8" or 3.2" were the common sizes used when ILI9341 code was tested

BillFM · Jun 25, 2025

Lavanya rajan said:
I'm using examples codes from this link https://github.com/vindar/tgx which contains programs related to T4.0, I uploaded few examples and all these are appearing inverted

I had similar inversion with tgx library using ST7789, 240x320, 2.8", parallel 8/16-bit. In one of the tgx files, I had to flip the "invert color" bit to fix the issue. I suspect you'll have to do the same fix. For IL9341, that's found in register 0x21.

KurtE · Jun 25, 2025

Lavanya rajan said:
Any input on how to sort out this issue

First suggestion, edit the file ILI9341_t3.cpp (library is installed by Teensyduino)

Look at the setRotation function:

Code:

void ILI9341_t3::setRotation(uint8_t m)
{
    rotation = m % 4; // can't be higher than 3
    beginSPITransaction(_clock);
    writecommand_cont(ILI9341_MADCTL);
    switch (rotation) {
    case 0:
        writedata8_last(MADCTL_MX | MADCTL_BGR);
        _width  = ILI9341_TFTWIDTH;
        _height = ILI9341_TFTHEIGHT;
        break;
    case 1:
        writedata8_last(MADCTL_MV | MADCTL_BGR);
        _width  = ILI9341_TFTHEIGHT;
        _height = ILI9341_TFTWIDTH;
        break;
    case 2:
        writedata8_last(MADCTL_MY | MADCTL_BGR);
        _width  = ILI9341_TFTWIDTH;
        _height = ILI9341_TFTHEIGHT;
        break;
    case 3:
        writedata8_last(MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_BGR);
        _width  = ILI9341_TFTHEIGHT;
        _height = ILI9341_TFTWIDTH;
        break;
    }
    endSPITransaction();
    cursor_x = 0;
    cursor_y = 0;
}

In this function change the instances of: MADCTL_BGR
to: MADCTL_RGB

save and try rebuilding your sketch and see if that solves it.

Lavanya rajan · Jun 25, 2025

KurtE said:

First suggestion, edit the file ILI9341_t3.cpp (library is installed by Teensyduino)

Look at the setRotation function:

Code:

void ILI9341_t3::setRotation(uint8_t m)
{
    rotation = m % 4; // can't be higher than 3
    beginSPITransaction(_clock);
    writecommand_cont(ILI9341_MADCTL);
    switch (rotation) {
    case 0:
        writedata8_last(MADCTL_MX | MADCTL_BGR);
        _width  = ILI9341_TFTWIDTH;
        _height = ILI9341_TFTHEIGHT;
        break;
    case 1:
        writedata8_last(MADCTL_MV | MADCTL_BGR);
        _width  = ILI9341_TFTHEIGHT;
        _height = ILI9341_TFTWIDTH;
        break;
    case 2:
        writedata8_last(MADCTL_MY | MADCTL_BGR);
        _width  = ILI9341_TFTWIDTH;
        _height = ILI9341_TFTHEIGHT;
        break;
    case 3:
        writedata8_last(MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_BGR);
        _width  = ILI9341_TFTHEIGHT;
        _height = ILI9341_TFTWIDTH;
        break;
    }
    endSPITransaction();
    cursor_x = 0;
    cursor_y = 0;
}

In this function change the instances of: MADCTL_BGR
to: MADCTL_RGB

save and try rebuilding your sketch and see if that solves it.

The issue related to colour inversion "The background color isn't displaying properly — I'm using fillScreen(RED), but the screen shows blue instead." has been sorted now with this solution, but still struggling with text inversion

Lavanya rajan · Jun 25, 2025

BillFM said:
I had similar inversion with tgx library using ST7789, 240x320, 2.8", parallel 8/16-bit. In one of the tgx files, I had to flip the "invert color" bit to fix the issue. I suspect you'll have to do the same fix. For IL9341, that's found in register 0x21.

previously it was 0x21 and now I changed to

#define ILI9341_INVOFF 0x20
#define ILI9341_INVON 0xFF
#define ILI9341_GAMMASET 0x26
#define ILI9341_DISPOFF 0x28
#define ILI9341_DISPON 0x29

but it is not sorted yet

Lavanya rajan · Jun 26, 2025

So, got this issue sorted out. In case, in future if anyone had this issue, modify the ILI9341_t3.cpp file.

look for setrotation function

Code:

switch (rotation) {
    case 0:
        writedata8_last(MADCTL_MX | MADCTL_RGB);
        _width  = ILI9341_TFTWIDTH;
        _height = ILI9341_TFTHEIGHT;
        break;
    case 1:
        writedata8_last(MADCTL_MV | MADCTL_RGB);
        _width  = ILI9341_TFTHEIGHT;
        _height = ILI9341_TFTWIDTH;
        break;
    case 2:
        writedata8_last(MADCTL_MY | MADCTL_RGB);
        _width  = ILI9341_TFTWIDTH;
        _height = ILI9341_TFTHEIGHT;
        break;
    case 3:
        writedata8_last(MADCTL_MX | MADCTL_MY | MADCTL_MV | MADCTL_RGB);
        _width  = ILI9341_TFTHEIGHT;
        _height = ILI9341_TFTWIDTH;
        break;
    }

In this function change the instances of: MADCTL_MX | MADCTL_RGB
to: !MADCTL_MX | MADCTL_RGB

KrisKasprzak · Jun 27, 2025

I tried your .ino on a Teensy 4.0
Arduino IDE 2.3.2
Teensyduino 1.57
ILI9341_t3 that delivers with Teensyduino
Add default compiler settings (600 mhz/faster)

using an ILI9341 with these 3 sizes: 2.2", 2.4" and 2.8"

All displays show a red background with text properly drawn

Not sure what the issue could be. Sorry,

honey_the_codewitch · Jun 27, 2025

There are variants if the ILI9341 that are basically compatible but require a slightly different initialization sequence.

TFT_eSPI handles these, so I would look there in Bodmer's defines - the init and rotation headers for the ILI9341 variants and you should find the sauce.

Lavanya rajan · Jun 27, 2025

KrisKasprzak said:
I tried your .ino on a Teensy 4.0
Arduino IDE 2.3.2
Teensyduino 1.57
ILI9341_t3 that delivers with Teensyduino
Add default compiler settings (600 mhz/faster)

using an ILI9341 with these 3 sizes: 2.2", 2.4" and 2.8"

All displays show a red background with text properly drawn

Not sure what the issue could be. Sorry,

Hello Sir,

I'm trying to use your number-keypad code (https://github.com/KrisKasprzak/Adafruit_ILI9341_Keypad), but during compilation of the code I'm having errors like

Code:

In file included from C:\Users\SMDDC 2\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\libraries\Adafruit_ILI9341_Keypad-main\Examples\Numberpad\Numberpad.ino:5:
C:\Users\SMDDC 2\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\libraries\Adafruit_ILI9341_Keypad-main/Adafruit_ILI9341_Keypad.h:197:29: error: section attribute not allowed for 'check'
  197 |         const unsigned char check [350] PROGMEM = {
      |                             ^~~~~
C:\Users\SMDDC 2\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\libraries\Adafruit_ILI9341_Keypad-main/Adafruit_ILI9341_Keypad.h:222:29: error: section attribute not allowed for 'backspace'
  222 |         const unsigned char backspace [210] PROGMEM = {
      |                             ^~~~~~~~~
C:\Users\SMDDC 2\AppData\Local\Arduino15\packages\teensy\hardware\avr\1.59.0\libraries\Adafruit_ILI9341_Keypad-main/Adafruit_ILI9341_Keypad.h:239:29: error: section attribute not allowed for 'cancel'
  239 |         const unsigned char cancel [350] PROGMEM = {
      |                             ^~~~~~
Multiple libraries were found for "XPT2046_Touchscreen.h"

How to sort this issue, make this code to run on T4.0

KrisKasprzak · Jun 29, 2025

What display lib are you using? The keypad you are trying to use is for the Adafruit_ILI9341 driver. If you are using the ILI9341_t3 driver, you need to use https://github.com/KrisKasprzak/ILI9341_t3_Keypad

BriComp · Jun 30, 2025

I tried the kayboard example in (https://github.com/KrisKasprzak/Adafruit_ILI9341_Keypad) and it gives the same result as noted by @Lavanya rajan noted above.

KrisKasprzak · Jun 30, 2025

Library fixed. I've made some internal changes as well to reduce memory consumption and speed things up. The init for the number pad includes and extra parameter. I would recommend deleted current installs of the ILI9341_t3_Keypad and getting the latest at

https://github.com/KrisKasprzak/ILI9341_t3_Keypad.

Examples updated as well and tested with Teensy 3.2 and Teensy 4.0.

BriComp · Jun 30, 2025

Problem still exists for the (https://github.com/KrisKasprzak/Adafruit_ILI9341_Keypad) which was/is the subject of the posts

mjs513 · Jun 30, 2025

BriComp said:
Problem still exists for the (https://github.com/KrisKasprzak/Adafruit_ILI9341_Keypad) which was/is the subject of the posts

Yeah but looks like op is using the ILI9341_t3 library from teensyduino so should be using the lib that @KrisKasprzak referenced

And yep looks like the adafruit version needs to be updated as well.

mjs513 · Jun 30, 2025

@KrisKasprzak

KrisKasprzak said:
Library fixed. I've made some internal changes as well to reduce memory consumption and speed things up. The init for the number pad includes and extra parameter. I would recommend deleted current installs of the ILI9341_t3_Keypad and getting the latest at

Just gave it a try on the micromod and keypad_numpad displays correctly.

Interface ILI9341 based TFT display with T4.0

Well-known member

Attachments

Senior Member+

Well-known member

Senior Member+

Well-known member

Senior Member+

Well-known member

Senior Member+

Well-known member

Senior Member+

Well-known member

Well-known member

Senior Member+

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Well-known member

Senior Member+

Senior Member+