====== Ultimate guide to ESP2866 pin/GPIO numbers ======
* https://espressif.com/en/products/hardware/esp8266ex/resources
* https://github.com/nodemcu/nodemcu-devkit-v1.0
* https://mintbox.in/media/esp-12e.pdf
^ Package pin number ^ Manufacturer name ^ GPIO number ^ Nodemcu name ^ Alternative functions ^ Notes ^
| 1 | VDDA |
| 2 | LNA |
| 3 | VDD3P3 |
| 4 | VDD3P3 |
| 5 | VDD_RTC |
| 6 | TOUT | | A0 | ADC | 0-1.0V raw, 0-3.2V nodemcu |
| 7 | CHIP_PU | | EN | Chip enable | High ON, Low OFF (with a small current consumed) |
| 8 | XPD_DCDC | GPIO16 | D0 | WAKE UP | Connect to EXT_RSTB (RESET) to support wakeup from deep-sleep. user/reset button on modemcu - pressed LOW, user LED on nodemcu - LOW ON, no interrupt/pwm/fancy features support - only I/O |
| 9 | MTMS | GPIO14 | D5 | HSPI_CLK, alternative I2C_SCL | |
| 10 | MTDI | GPIO12 | D6 | HSPI_MISO | |
| 11 | VDDPST |
| 12 | MTCK | GPIO13 | D7 | HSPI_MOSI, UART0_CTS, alternative UART0_RX | To use alternative function please see manufacturer doc |
| 13 | MTDO | GPIO15 | D8 | HSPI_CS, UART0_RTS, alternative USART0_TX | To use alternative function please see manufacturer doc, keep LOW during boot |
| 14 | GPIO2 | GPIO2 | D4 | USART1_TX, alternative I2C_SDA | May print garbage during boot/programming, keep HIGH during boot |
| 15 | GPIO0 | GPIO0 | D3 | SPI_CS2 | On nodemcu run/flash selector - run HIGH, flash LOW |
| 16 | GPIO4 | GPIO4 | D2 | | |
| 17 | VDDPST |
| 18 | SDIO_DATA_2 | GPIO9 | SD2 (D11) | SD_D2 | Connected to flash in most modules |
| 19 | SDIO_DATA_3 | GPIO10 | SD3 (D12) | SD_D3 | Connected to flash in most modules |
| 20 | SDIO_CMD | GPIO11 | CMD | SD_CMD | Connected to flash in most modules |
| 21 | SDIO_CLK | GPIO6 | CLK | SD_CLK | Connected to flash in most modules |
| 22 | SDIO_DATA_0 | GPIO7 | SD0 | SD_D0 | Connected to flash in most modules |
| 23 | SDIO_DATA_1 | GPIO8 | SD1 | SD_D1 | Connected to flash in most modules |
| 24 | GPIO5 | GPIO5 | D1 | | |
| 25 | U0RXD | GPIO3 | D9 | UART0_RX | UART RX during programming |
| 26 | U0TXD | GPIO1 | D10 | UART0_TX, SPI_CS1 | UART TX during programming |
| 27 | XTAL_OUT |
| 28 | XTAL_IN |
| 29 | VDDD |
| 30 | VDDA |
| 31 | RES12K | | | | Connect to ground with 12kΩ resistor |
| 32 | EXT_RSTB | | RST | Reset | External reset, reset LOW, active HIGH |