Overview

The ESP8266EX is the groundbreaking 32-bit Wi-Fi System-on-Chip (SoC) manufactured by Espressif Systems. Responsible for triggering the low-cost Wi-Fi IoT revolution, it integrates a 32-bit Tensilica L106 microcontroller core running at 80 MHz…160 MHz80\text{ MHz} \dots 160\text{ MHz}, a complete 802.11b/g/n802.11\text{b/g/n} Wi-Fi radio, power amplifier, low-noise receiver amplifier, transmit/receive switch, and TCP/IP protocol stack.

Found bare on QFN-32 packages and packaged inside ESP-01, ESP-12F, NodeMCU, and Wemos D1 Mini module boards, the ESP8266EX connects microcontrollers to the internet or acts as a standalone host MCU programmed via Arduino IDE, MicroPython, or ESPHome.

Quick reference

CPU Architecture32-bit Tensilica L106 32-bit RISC core (80 MHz…160 MHz80\text{ MHz} \dots 160\text{ MHz})
Wi-Fi Standards802.11 b/g/n802.11\text{ b/g/n} (2.4 GHz…2.5 GHz2.4\text{ GHz} \dots 2.5\text{ GHz})
Transmitter Output Power+20 dBm+20\text{ dBm} (802.11b mode) / +17 dBm+17\text{ dBm} (802.11g)
Operating Voltage (VDD)2.5 V to 3.6 V DC (3.3 V nominal)
Memory Architecture160 KB160\text{ KB} internal SRAM (80 KB80\text{ KB} User RAM), External SPI Flash (1MB…16MB1\text{MB} \dots 16\text{MB})
Sleep Power Consumption<10 μA< 10\ \mu\text{A} (Deep Sleep mode)
ADC Channel10-bit ADC channel (0V…1.0V0\text{V} \dots 1.0\text{V} raw IC input)
Package32-pin QFN (5×5 mm5 \times 5\text{ mm}) / ESP-12F Module

Pinout (ESP-12F Module Form Factor)

text
                       ┌─────────────┐
                [REST] │             │ [ADC  ] (A0 - 10-bit ADC)
                 [CH_PD]│   ESP-12F   │ [EN   ] (Chip Enable)
                 [GPIO16]│  ESP8266EX  │ [GPIO14] (HSPI_CLK)
                 [GPIO14]│             │ [GPIO12] (HSPI_MISO)
                 [GPIO12]│             │ [GPIO13] (HSPI_MOSI)
                 [GPIO13]│             │ [VCC  ] (3.3V)
                 [VCC   ]│             │ [CS0  ]
                 [CS0   ]│             │ [MISO ]
                 [MISO  ]│             │ [GPIO9 ]
                 [GPIO9 ]│             │ [GPIO10]
                 [GPIO10]│             │ [MOSI ]
                 [MOSI  ]│             │ [SCLK ]
                 [SCLK  ]│             │ [GND  ]
                 [GND   ]│             │ [GPIO15] (Boot Pin - Pull LOW)
                 [GPIO2 ]│             │ [GPIO0 ] (Boot Pin - Flashing)
                 [GPIO4 ]│             │ [GPIO5 ]
                 [RXD0  ]│             │ [TXD0  ]
                       └─────────────┘

Specifications

ParameterSymbolMinTypMaxUnitConditions
Supply VoltageVDDV_{DD}2.53.33.6VDC supply
TX Current (802.11b +20dBm)ITXI_{TX}—170220mAContinuous RF transmit
RX CurrentIRXI_{RX}—5056mAContinuous RF receive
Deep Sleep CurrentIsleepI_{sleep}—1020µARTC timer active
Standby CurrentIstbyI_{stby}—0.91.2mALight sleep mode

Boot Mode Pin Selection Table

For the ESP8266EX to boot correctly from SPI Flash, specific GPIO boot pins must be pulled High or Low at power-on:

Boot ModeGPIO15GPIO0GPIO2
UART Flashing (Download Code)LOW (GND)LOW (GND)HIGH (3.3V)
Normal Flash Boot (Execute Code)LOW (GND)HIGH (3.3V)HIGH (3.3V)
SDIO BootHIGH (3.3V)AnyAny
Important

ESP8266 Chip Enable (EN / CH_PD): Pin EN (CH_PD) MUST be pulled High to 3.3V via a 10 kΩ10\ \text{k}\Omega resistor for the chip to power on. Leaving EN floating keeps the chip in shutdown mode.

Example (Arduino ESP8266 Wi-Fi Station Scanner)

cpp
#include <ESP8266WiFi.h>

void setup() {
  Serial.begin(115200);
  WiFi.mode(WIFI_STA);
  WiFi.disconnect();
  delay(100);

  Serial.println("ESP8266EX Wi-Fi Network Scanner");
}

void loop() {
  Serial.println("Scanning Wi-Fi networks...");
  int n = WiFi.scanNetworks();

  if (n == 0) {
    Serial.println("No networks found.");
  } else {
    Serial.print(n); Serial.println(" networks found:");
    for (int i = 0; i < n; ++i) {
      Serial.print(i + 1); Serial.print(": ");
      Serial.print(WiFi.SSID(i)); Serial.print(" (");
      Serial.print(WiFi.RSSI(i)); Serial.println(" dBm)");
    }
  }

  delay(5000);
}

Common mistakes

  • Powering from Arduino 3.3V pin: The ESP8266EX requires up to 220 mA…300 mA220\text{ mA} \dots 300\text{ mA} continuous current during Wi-Fi transmission spikes. The onboard 3.3V regulator on older Arduino Uno boards can only supply 50 mA50\text{ mA}, causing brownout reset loops. Power from a dedicated 3.3V 500mA LDO (like AMS1117-3.3).
  • Applying 5.0V to GPIO pins: The ESP8266EX is NOT 5V tolerant. Connecting 5V signals directly to GPIO pins degrades and damages the chip over time. Use resistor voltage dividers or bidirectional level shifters.

Notes

  • ESP8266EX vs ESP32: ESP8266EX is single-core 80MHz with 2.4GHz Wi-Fi; ESP32 is dual-core 240MHz with Wi-Fi + Bluetooth LE.

Assets & downloads