Wiring for your board

Pins belong to your microcontroller

Two controls. The top one changes every number on the drawing. The bottom one, the size of the display board, changes nothing at all, and that is the thing worth sitting with for a moment.

The GPIO a wire lands on is a property of the microcontroller you are compiling for. The driver chip, the resolution, the offsets and the backlight polarity are properties of the glass. They never meet, so there is no combination to look up: pick your microcontroller, pick your display, and the two answers are independent.

The library goes further and picks the row for you, from what you selected in Tools ▸ Board. Compile for an ESP32-S3 and you get the S3 pins; compile for an ESP32 Dev Module and you get the classic ones. Nothing to edit. The defaults are the pins of the Lonely Binary breakout; if you wire the eight holes to other GPIOs, that is what setWiring() is for.

The gap in the table

There are two rows and no third one. The library chooses the S3 row when it is built for an S3, and the classic-ESP32 row otherwise.

Otherwise includes the ESP32-C3, and the classic row hands out GPIO 23 for data and GPIO 32 for the backlight. A C3's pins stop at GPIO 21. Neither of those exists.

So on a C3, and on anything else that is not one of the two named chips, the default pins are not a starting point. In the version of the library tested for this book, built against arduino-esp32 3.3.10, a C3 does not get as far as wrong pins: the classic row names the VSPI bus, which a C3 does not have, and the compile stops. The library says it is for the two chips and nothing else.

The override below is for what it is for: an ESP32 or ESP32-S3 whose default pins are taken by something else.

LB_Wiring pins = LB_WIRING;   // start from the default for this chip
pins.cs   = 5;                // ...then change what your board actually has
pins.dc   = 16;
pins.rst  = 17;
pins.mosi = 23;
pins.sclk = 18;
pins.backlight = 4;

display.setWiring(pins);      // before begin()
display.begin();

The same call is how you tell the library that a hole is not wired. With the CS or BL solder jumper bridged, set pins.cs or pins.backlight to -1 so nothing drives the pad.

Copy LB_WIRING rather than declaring an empty one. It carries an SPI bus number whose meaning is not the same on every chip, and starting from the default gives you a bus that is already correct for the chip you are building for.

printInfo() prints the pins actually in use and marks any you overrode, which turns a wiring mistake into a line in the serial log instead of a blank screen.

More than one display

Clock and data are shared, and each display gets its own CS. That is ordinary SPI, and it is the reason CS exists: without it, two displays on one bus both take every byte. Give each its own RST too, because a reset pulse reaches every display wired to it.