ST7789 driven by ESP32-S2 in parallel mode fails `TFT_ReadWrite_Test` diagnostic

[chris-at-redfernsolutions]

Issue

We are trying to use this ST7789-based display on a custom board based around the ESP32-S2. The diagnostic examples/Tests and diagnostics/TFT_ReadWrite_Test fails to read data back.

Wiring

Our wiring is like so:

Note that our connector is flipped 180°, so pin 24 on our schematic corresponds to pin 1 on the datasheet:

Name	LEDA	LEDK	GND	VDD-2V8	VDDIO	IMI/2	RESET	CS	D/C	WR	RD	SDA	DB0	DB1	DB2	DB3	DB4	DB5	DB6	DB7	TE	NC	GND	GND
Our board	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1
Datasheet	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24

The connector orientation is correct because we can manually GPIO the backlight to turn it on:

digitalWrite(PIN_LCD_PWR_EN, 0);        
digitalWrite(PIN_LCD_K, 0);
digitalWrite(PIN_LCD_A, 1);

Configuration

Our firmware versions are:

Tool	Version
Arduino IDE	2.0.3
Arduino-ESP32 core	2.0.5
TFT_eSPI	2.4.79

We only have access the 'parallel' (8080) IO mode, because IMI/2 is permantently tied to ground. Thus, our User_Setup.h contains:

#define USER_SETUP_INFO "User_Setup"

#define TFT_PARALLEL_8_BIT
#define ST7789

#define TFT_RGB_ORDER TFT_RGB  // Colour order Red-Green-Blue

#define TFT_WIDTH  240 // ST7789 240 x 240 and 240 x 320
#define TFT_HEIGHT 240 // ST7789 240 x 240

#define TFT_CS   13  
#define TFT_DC   12  
#define TFT_RST  14  

#define TFT_WR    11  
#define TFT_RD    10  

#define TFT_D0   9  
#define TFT_D1   8  
#define TFT_D2   7  
#define TFT_D3   6  
#define TFT_D4   5
#define TFT_D5   4
#define TFT_D6   3
#define TFT_D7   2

#define LOAD_GLCD   
#define LOAD_FONT2  
#define LOAD_FONT4  
#define LOAD_FONT6  
#define LOAD_FONT7  
#define LOAD_FONT8  
#define LOAD_GFXFF  
#define SMOOTH_FONT

#define SPI_FREQUENCY  27000000
#define SPI_READ_FREQUENCY  20000000
#define SPI_TOUCH_FREQUENCY  2500000

Testing

Attached are our .ino and User_Setup.h files: example.zip

The sketch examples/Tests and diagnostics/Read_User_Setup gives the following output:

TFT_eSPI ver = 2.4.79
Processor    = ESP32
Frequency    = 240MHz
Transactions = Yes
Interface    = Parallel
Display driver = 778B
Display width  = 240
Display height = 240

TFT_CS   = GPIO 13
TFT_DC   = GPIO 12
TFT_RST  = GPIO 14
TFT_WR   = GPIO 11
TFT_RD   = GPIO 10

TFT_D0   = GPIO 9
TFT_D1   = GPIO 8
TFT_D2   = GPIO 7
TFT_D3   = GPIO 6
TFT_D4   = GPIO 5
TFT_D5   = GPIO 4
TFT_D6   = GPIO 3
TFT_D7   = GPIO 2

Font GLCD   loaded

The sketch examples/Tests and diagnostics/TFT_ReadWrite_Test gives this output:

Pixel value written = 80
Pixel value read    = 0
ERROR                 ^^^^
Pixel value written = 100
Pixel value read    = 0
ERROR                 ^^^^

When powered on while running the TFT_ReadWrite_Test, the LCD backlight initially turns on showing a grey screen. The display then subtly alternates in brightness about 10 times over the course of 2 seconds. This suggests that the display is at least receiving some commands!

Debugging attempts

Changing tft.fillScreen(TFT_BLACK); to TFT_RED or TFT_WHITE has no discernible effect.

• As suggested in this thread, we tried switching from ST7789_DRIVER to ST7789_2_DRIVER in User_Setup.h. This had no effect.

• As per this thread, we attempted:

  • Switching from ST7789_Driver to ILI9486_DRIVER [no effect]
  • Inserting tft.begin() after tft.init() in our .ino sketch [no effect]
  • Enabling TFT_SDA_READ [no effect]

---

Additionally, could someone clarify if extra work is required to make the library work with an ESP32-S2, or is it automatically detected? I noticed that some parts of the library are specifically written for ESP32-C3 / ESP32-S3 etc. but there is little mention of the S2.

[Bodmer]

The S2 has been tested with for SPI displays only.

The original ESP32 and ESP32 S3 can be used with 8 bit parallel screens.

[Bodmer]

I will update the ReadMe with a table later to show which processor and which interfaces are supported for each.

[Bodmer]

I have had a look at the ESP32 code and I see that the code for running the ESP32 S2 with a parallel 8 bit display is present and looks correct so it should work. However I have not tested it so I will connect up a display and see if it needs any changes.

[Bodmer]

I have connected up and tested 2 displays (ILI9341 and ILI9481) with an 8 bit parallel interface and they work fine. I do not have an ST7789 with a parallel interface to test but world expect it to work. This is my setup file:

#define ILI9341_DRIVER
//#define ILI9486_DRIVER

#define TFT_PARALLEL_8_BIT

#define TFT_RST    9
#define TFT_CS    10
#define TFT_DC    11
#define TFT_WR    12
#define TFT_RD    13

#define TFT_D0   1
#define TFT_D1   2
#define TFT_D2   3
#define TFT_D3   4
#define TFT_D4   5
#define TFT_D5   6
#define TFT_D6   7
#define TFT_D7   8

#define LOAD_GLCD
#define LOAD_FONT2
#define LOAD_FONT4
#define LOAD_FONT6
#define LOAD_FONT7
#define LOAD_FONT8
#define LOAD_GFXFF

#define SMOOTH_FONT

[Bodmer]

I have also now run the TFT_ReadWrite_Test and it works fine too.

The ST7789V has been tested with an ESP32 S3 with 8 bit parallel interface so I would expect your setup to work. This all suggests there is an electrical problem with your setup.

[Lawrence-RedFern]

Hi Bodmer, thanks for testing this.

In the file TFT_eSPI.h, which processor did you have defined for testing the ESP32-S2?

#if defined(CONFIG_IDF_TARGET_ESP32S3)
  #include "Processors/TFT_eSPI_ESP32_S3.h"
#elif defined(CONFIG_IDF_TARGET_ESP32C3)
  #include "Processors/TFT_eSPI_ESP32_C3.h"
#elif defined (ESP32)
  #include "Processors/TFT_eSPI_ESP32.h"
#elif defined (ARDUINO_ARCH_ESP8266)
  #include "Processors/TFT_eSPI_ESP8266.h"
#elif defined (STM32)
  #include "Processors/TFT_eSPI_STM32.h"
#elif defined(ARDUINO_ARCH_RP2040)
  #include "Processors/TFT_eSPI_RP2040.h"
#else
  #include "Processors/TFT_eSPI_Generic.h"
#endif

[Bodmer]

This is the include file, it supports both ESP32 and S2:

include "Processors/TFT_eSPI_ESP32.h"