Hardware SPI don't work with ILI9341 - 3 bugs and 3 solutions here

[Rémy LUCAS]

Hi,

I'm use the Adafruit_ILI9341 and the GFX library to drive a ILI9341 TFT SPI touch screen on a Arduino UNO with an Ethernet Shield 2 (for the touch pad I use URTouch.h)

I've found some bugs and also solutions :

1st :
If you use
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC, TFT_RST)
you've got an error "call of overloaded 'Adafruit_ILI9341(int, int, int)' is ambiguous"
So you have to edit Adafruit_ILI9341.h and Adafruit_ILI9341.cpp to comment Adafruit_ILI9341() fonctions for ESP8266
I think you have to change function names to avoid this.

2nd :
ILI9341 use SPI MODE 3 and cannot work with the default SPI MODE the library uses with hardware SPI
Curiously, the software SPI use the good mode.
Thus, you have to edit Adafruit_ILI9341.cpp and replace
initSPI(freq);
by
initSPI(freq, SPI_MODE3);

3rd
When you have quite long wires (eg. 20cm dupont wire) and slow 5V/3.3V level converter (or just 10K resistors !) from the Arduino UNO and the TFT you've got a speed limitation.
Remember that in electronics :

• long wire = coil = low pass filter
• resistor + logical input capacitance = low pass filter
  Indeed, in the sketch, you have to use
  tft.begin(3000000);
  instead of
  tft.begin();

You can also use a fast SPI speed with short wires and a hi-speed level converter.

I found that a lot of people don't know these problems and use
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC, TFT_MOSI, TFT_CLK, TFT_RST, TFT_MISO);
with the hardware SPI pins...
that's very very bad...
that's very slow...
and it doesn't work with other SPI devices...

I wonder that the constructor have explicit names as "tftHardwareSPI" and "tftSoftwareSPI"

Please, can you update your library and also your documentation and sample codes ?

Bests regards.

[OLderDan63]

spi mode 3 fixed my hardware spi issues, thankyou so much for this.

[Colin G(IO)]

I also have a hardware SPI bug. Maybe this is bug 4.
I am using this library with an Arduino Giga R1. I was trying to get this library to work with SPI1 but was having problems.

It works when I try the default SPI port using the following:

// Use hardware SPI (on Uno, #13, #12, #11) and the above for CS/DC
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC);

But if I then add in the SPI Class it fails to work - I just get a dimmer white screen with very faint flicker (this is the same result if I use &SPI1):

Adafruit_ILI9341 tft = Adafruit_ILI9341(&SPI, TFT_CS, TFT_DC);

[Colin G(IO)]

I discovered my issue. The library has DC and CS pins swapped, when using Adafruit_ILI9341(SPIClass *spiClass, int8_t dc, int8_t cs = -1, int8_t rst = -1);