TFT_eSPI: readPixel() troubles

[Matt_TYGA]

Hi Guys.

Hardware: ESP32 with 4.0" TFT (with touch but not used). ST7796

Using TFT_eSPI Library

My setting:

// For ST7796 Setting_Matt//

#define TFT_MISO 16
#define TFT_MOSI 23
#define TFT_SCLK 18
#define TFT_CS   15  // Chip select control pin
#define TFT_DC    2  // Data Command control pin
#define TFT_RST   4  // Reset pin (could connect to RST pin)

 #define SPI_FREQUENCY  40000000
#define SPI_READ_FREQUENCY  15000000

I'm just trying to read a pixel and then put a filled rectangle on the display.

I came to the #define SPI_READ_FREQUENCY 15000000 by just messing about with frequency until the serial output had constant 0x07E0 output.

However, I need a delay(2); after the tft.readPixel(); Anything smaller than 2ms delay and I just get a green screen. It appears to run through the code as a get an output on the serial monitor, but never changes to a black screen with my filled rectangle.

Could it be my display not capable? I don't really understand.

If I use a read frequency higher than 15MHz then the colour is wrong.

This is not the real code that I want, but I'm just trying to understand how to use the function.

Having delays in the code is not an option, so I can't implement it like this.

Any assistance more than welcome.

Here's the code I'm using for test:

#include <SPI.h>
#include <TFT_eSPI.h>

uint16_t x;

TFT_eSPI tft = TFT_eSPI();

void setup() {
  Serial.begin(115200);
  tft.init();
}

void loop() {

  tft.fillScreen(TFT_GREEN);
  x = tft.readPixel(100, 100);
  // delay(1);  //  This delay of 1ms does not work. If I remove delay completely it doesn't work. I just get a green screen
  delay(2);  //  This works.
  tft.fillScreen(TFT_BLACK);
  tft.fillRect(100, 100, 100, 100, x);
  delay(1000);
}

Thanks in advance for any help.

Cheers,

Matt

[MaximoEsfuerzo]

Try with

#define SPI_READ_FREQUENCY  13400000

Souce ST7796 readPixel issue · Issue #1305 · Bodmer/TFT_eSPI · GitHub

[Matt_TYGA]

@MaximoEsfuerzo

Thanks for your answer. At 15MHz I appear to be getting the correct colour but if I do not put a 2ms delay after the tft.readPixel() then the tft.fillScreen(TFT_BLACK)​ code never works and the screen stays filled with green.

I

Matt