ESP8266EX - Espressif Systems

ESP8266EX

Datasheet

Version 5.9

Espressif Systems

About This Guide

This document introduces the speciﬁcations of ESP8266EX.

Release Notes

Date

Version

Release Notes

2015.12

V4.6

Updated Chapter 3.

2016.02

V4.7

Updated Section 3.6 and Section 4.1.

2016.04

V4.8

Updated Chapter 1.

2016.08

V4.9

Updated Chapter 1.

2016.11

V5.0

Added Appendix Ⅱ “Learning Resources”.

2016.11

V5.1

Changed the power consumption during Deep-sleep from 10 μA to 20 μA

in Table 5-2.

2016.11

V5.2

Changed the crystal frequency range from “26 MHz to 52 MHz” to “24

MHz to 52 MHz” in Section 3.3.

2016.12

V5.3

Changed the minimum working voltage from 3.0V to 2.5V.

2017.04

V5.4

Changed chip input and output impedance from 50Ω to 39+j6 Ω.

2017.10

V5.5

Updated Chapter 3 regarding the range of clock amplitude to 0.8 ~ 1.5V.

2017.11

V5.6

Updated VDDPST from 1.8V ~ 3.3V to 1.8V ~ 3.6V.

2017.11

V5.7

•Corrected a typo in the description of SDIO_DATA_0 in Table 2-1;

•Added the testing conditions for the data in Table 5-2.

2018.02

V5.8

•Updated Wi-Fi protocols in Section 1.1;

•Updated description of the integrated Tensilica processor in 3.1.

2018.09

V5.9

•Update document cover;

•Added a note for Table 1-1;

•Updated Wi-Fi key features in Section 1.1;

•Updated description of the Wi-Fi function in 3.5;

•Updated pin layout diagram;

•Fixed a typo in Table 2-1;

•Removed Section AHB and AHB module;

•Restructured Section Power Management;

•Fixed a typo in Section UART;

•Removed description of transmission angle in Section IR Remote

Control;

•Other optimization (wording).

Documentation Change Notiﬁcation

Espressif provides email notiﬁcations to keep customers updated on changes to

technical documentation. Please subscribe at https://www.espressif.com/en/subscribe.

Certiﬁcation

Download certiﬁcates for Espressif products from https://www.espressif.com/en/

certiﬁcates.!

Table of Contents 
Overview  1 ................................................................................................................................
1. Wi-Fi Key Features!1".....................................................................................................................
2. Speciﬁcations!2".............................................................................................................................
3. Applications!3"...............................................................................................................................
Pin Deﬁnitions  4 ........................................................................................................................
Functional Description  6 ..........................................................................................................
1. CPU, Memory, and Flash!6"...........................................................................................................
1.1. CPU!6"...............................................................................................................................
1.2. Memory!6"..........................................................................................................................
1.3. External Flash!7"................................................................................................................
2. Clock!7"..........................................................................................................................................
2.1. High Frequency Clock!7"...................................................................................................
2.2. External Clock Requirements!8"........................................................................................
3. Radio!8"..........................................................................................................................................
3.1. Channel Frequencies!8".....................................................................................................
3.2. 2.4 GHz Receiver!9"...........................................................................................................
3.3. 2.4 GHz Transmitter!9".......................................................................................................
3.4. Clock Generator!9"............................................................................................................
4. Wi-Fi!9"...........................................................................................................................................
4.1. Wi-Fi Radio and Baseband!9"............................................................................................
4.2. Wi-Fi MAC!10"...................................................................................................................
5. Power Management!10".................................................................................................................
Peripheral Interface  12 .............................................................................................................
1. General Purpose Input/Output Interface (GPIO)!12"......................................................................
2. Secure Digital Input/Output Interface (SDIO)!12"...........................................................................
3. Serial Peripheral Interface (SPI/HSPI)!13"......................................................................................
3.1. General SPI (Master/Slave)!13"..........................................................................................
3.2. HSPI (Slave)!13".................................................................................................................
4. I2C Interface!14".............................................................................................................................
5. I2S Interface!14".............................................................................................................................
6. Universal Asynchronous Receiver Transmitter (UART)!14"............................................................
7. Pulse-Width Modulation (PWM)!15"...............................................................................................
8. IR Remote Control!16"....................................................................................................................
9. ADC (Analog-to-Digital Converter)!16"...........................................................................................

5. Electrical Speciﬁcations  18 ......................................................................................................
5.1. Electrical Characteristics!18"..........................................................................................................
5.2. RF Power Consumption!18"...........................................................................................................
5.3. Wi-Fi Radio Characteristics!19".....................................................................................................
6. Package Information  20 ...........................................................................................................
I. Appendix - Pin List  21 ..............................................................................................................
II. Appendix - Learning Resources  22 .........................................................................................
II.1. Must-Read Documents!22"............................................................................................................
II.2. Must-Have Resources!22..............................................................................................................

1. Overview

Espressif’s ESP8266EX delivers highly integrated Wi-Fi SoC solution to meet users’

continuous demands for efﬁcient power usage, compact design and reliable performance

in the Internet of Things industry.

With the complete and self-contained Wi-Fi networking capabilities, ESP8266EX can

perform either as a standalone application or as the slave to a host MCU. When

ESP8266EX hosts the application, it promptly boots up from the ﬂash. The integrated high-

speed cache helps to increase the system performance and optimize the system memory.

Also, ESP8266EX can be applied to any microcontroller design as a Wi-Fi adaptor through

SPI/SDIO or UART interfaces.

ESP8266EX integrates antenna switches, RF balun, power ampliﬁer, low noise receive

ampliﬁer, ﬁlters and power management modules. The compact design minimizes the PCB

size and requires minimal external circuitries.

Besides the Wi-Fi functionalities, ESP8266EX also integrates an enhanced version of

Tensilica’s L106 Diamond series 32-bit processor and on-chip SRAM. It can be interfaced

with external sensors and other devices through the GPIOs. Software Development Kit

(SDK) provides sample codes for various applications.

Espressif Systems’ Smart Connectivity Platform (ESCP) enables sophisticated features

including:

•Fast switch between sleep and wakeup mode for energy-efﬁcient purpose;

•Adaptive radio biasing for low-power operation

•Advance signal processing

•Spur cancellation and RF co-existence mechanisms for common cellular, Bluetooth,

DDR, LVDS, LCD interference mitigation

1.1. Wi-Fi Key Features

•802.11 b/g/n support

•802.11n support (2.4 GHz), up to 72.2 Mbps

•Defragmentation

•2 x virtual Wi-Fi interface

•Automatic beacon monitoring (hardware TSF)

•Support Infrastructure BSS Station mode/SoftAP mode/Promiscuous mode

•Antenna diversity!

Espressif

$/$1 24

2018.09

1. Overview

1.2. Speciﬁcations

Table 1-1. Speciﬁcations

Categories

Items

Parameters

Wi-Fi

Certiﬁcation

Wi-Fi Alliance

Protocols

802.11 b/g/n (HT20)

Frequency Range

2.4G ~ 2.5G (2400M ~ 2483.5M)

TX Power

802.11 b: +20 dBm

802.11 g: +17 dBm

802.11 n: +14 dBm

Rx Sensitivity

802.11 b: –91 dbm (11 Mbps)

802.11 g: –75 dbm (54 Mbps)

802.11 n: –72 dbm (MCS7)

Antenna

PCB Trace, External, IPEX Connector, Ceramic Chip

Hardware

CPU

Tensilica L106 32-bit processor

Peripheral Interface

UART/SDIO/SPI/I2C/I2S/IR Remote Control

GPIO/ADC/PWM/LED Light & Button

Operating Voltage

2.5V ~ 3.6V

Operating Current

Average value: 80 mA

Operating Temperature Range

–40°C ~ 125°C

Package Size

QFN32-pin (5 mm x 5 mm)

External Interface

Software

Wi-Fi Mode

Station/SoftAP/SoftAP+Station

Security

WPA/WPA2

Encryption

WEP/TKIP/AES

Firmware Upgrade

UART Download / OTA (via network)

Software Development

Supports Cloud Server Development / Firmware and SDK

for fast on-chip programming

Network Protocols

IPv4, TCP/UDP/HTTP

User Conﬁguration

AT Instruction Set, Cloud Server, Android/iOS App

📖 Note:

The TX power can be conﬁgured based on the actual user scenarios.

Espressif

$/$2 24

2018.09

1. Overview

1.3. Applications

•Home appliances

•Home automation

•Smart plugs and lights

•Industrial wireless control

•Baby monitors

•IP cameras

•Sensor networks

•Wearable electronics

•Wi-Fi location-aware devices

•Security ID tags

•Wi-Fi position system beacons!

Espressif

$/$3 24

2018.09

2. Pin Deﬁnitions

Figure 2-1 shows the pin layout for 32-pin QFN package.

Figure 2-1. Pin Layout (Top View)

Table 2-1 lists the deﬁnitions and functions of each pin.

XDP_DCDC

CHIP_EN

TOUT

VDD_RTC

VDD3P3

LNA

VDDA

24 GPIO5

U0RXD

U0TXD

XTAL_OUT

XTAL_IN

VDDA

RES12K

EXT_RSTB

GPIO4

GPIO0

GPIO2

MTDO

MTCK

VDDPST

MTDI

MTMS

ESP8266EX

SD_DATA_2

SD_DATA_3

SD_CMD

SD_CLK

SD_DATA_0

SD_DATA_1

VDDD

VDDPST

33 GND

Table 2-1. ESP8266EX Pin Deﬁnitions

Name

Type

Function

VDDA

Analog Power 2.5V ~ 3.6V

LNA

I/O

RF antenna interface

Chip output impedance=39+j6 Ω. It is suggested to retain the

π-type matching network to match the antenna.

VDD3P3

Ampliﬁer Power 2.5V ~ 3.6V

VDD3P3

Ampliﬁer Power 2.5V ~ 3.6V

VDD_RTC

NC (1.1V)

TOUT

ADC pin. It can be used to test the power-supply voltage of

VDD3P3 (Pin3 and Pin4) and the input power voltage of TOUT

(Pin 6). However, these two functions cannot be used

simultaneously.

Espressif

$/$4 24

2018.09

2. Pin Deﬁnitions

CHIP_EN

Chip Enable

High: On, chip works properly

Low: Off, small current consumed

XPD_DCDC

I/O

Deep-sleep wakeup (need to be connected to EXT_RSTB);

GPIO16

MTMS

I/O

GPIO 14; HSPI_CLK

MTDI

I/O

GPIO 12; HSPI_MISO

VDDPST

Digital/IO Power Supply (1.8V ~ 3.6V)

MTCK

I/O

GPIO 13; HSPI_MOSI; UART0_CTS

MTDO

I/O

GPIO 15; HSPI_CS; UART0_RTS

GPIO2

I/O

UART TX during ﬂash programming; GPIO2

GPIO0

I/O

GPIO0; SPI_CS2

GPIO4

I/O

GPIO4

VDDPST

Digital/IO Power Supply (1.8V ~ 3.6V)

SDIO_DATA_2

I/O

Connect to SD_D2 (Series R: 200Ω); SPIHD; HSPIHD; GPIO9

SDIO_DATA_3

I/O

Connect to SD_D3 (Series R: 200Ω); SPIWP; HSPIWP;

GPIO10

SDIO_CMD

I/O

Connect to SD_CMD (Series R: 200Ω); SPI_CS0; GPIO11

SDIO_CLK

I/O

Connect to SD_CLK (Series R: 200Ω); SPI_CLK; GPIO6

SDIO_DATA_0

I/O

Connect to SD_D0 (Series R: 200Ω); SPI_MISO; GPIO7

SDIO_DATA_1

I/O

Connect to SD_D1 (Series R: 200Ω); SPI_MOSI; GPIO8

GPIO5

I/O

GPIO5

U0RXD

I/O

UART Rx during ﬂash programming; GPIO3

U0TXD

I/O

UART TX during ﬂash programming; GPIO1; SPI_CS1

XTAL_OUT

I/O

Connect to crystal oscillator output, can be used to provide BT

clock input

XTAL_IN

I/O

Connect to crystal oscillator input

VDDD

Analog Power 2.5V ~ 3.6V

VDDA

Analog Power 2.5V ~ 3.6V

RES12K

Serial connection with a 12 kΩ resistor and connect to the

ground

EXT_RSTB

External reset signal (Low voltage level: active)

Name

Type

Function

📖 Note:

GPIO2, GPIO0, and MTDO are used to select booting mode and the SDIO mode.

Espressif

$/$5 24

2018.09

3. Functional Description

The functional diagram of ESP8266EX is shown as in Figure 3-1.

Figure 3-1. Functional Block Diagram

3.1. CPU, Memory, and Flash

3.1.1. CPU

The ESP8266EX integrates a Tensilica L106 32-bit RISC processor, which achieves extra-

low power consumption and reaches a maximum clock speed of 160 MHz. The Real-Time

Operating System (RTOS) and Wi-Fi stack allow 80% of the processing power to be

available for user application programming and development. The CPU includes the

interfaces as below:

•Programmable RAM/ROM interfaces (iBus), which can be connected with memory

controller, and can also be used to visit ﬂash.

•Data RAM interface (dBus), which can connected with memory controller.

•AHB interface which can be used to visit the register.

3.1.2. Memory

ESP8266EX Wi-Fi SoC integrates memory controller and memory units including SRAM

and ROM. MCU can access the memory units through iBus, dBus, and AHB interfaces. All

memory units can be accessed upon request, while a memory arbiter will decide the

running sequence according to the time when these requests are received by the

processor.

According to our current version of SDK, SRAM space available to users is assigned as

below.

RF balun

Switch

receive

transmit

Analog

receive

Analog

transmit

PLL VCO 1/2 PLL

Digital baseband

MAC Interface

PMU Crystal Bias circuits SRAM PMU

SDIO

I2C

PWM

ADC

SPI

UART

GPIO

I2S

Flash

Registers

CPU

Sequencers

Accelerator

Espressif

$/$6 24

2018.09

3. Functional Description

•RAM size < 50 kB, that is, when ESP8266EX is working under the Station mode and

connects to the router, the maximum programmable space accessible in Heap +

Data section is around 50 kB.

•There is no programmable ROM in the SoC. Therefore, user program must be stored

in an external SPI ﬂash.

3.1.3. External Flash

ESP8266EX uses external SPI ﬂash to store user programs, and supports up to 16 MB

memory capacity theoretically.

The minimum ﬂash memory of ESP8266EX is shown below:

•OTA disabled: 512 kB at least

•OTA enabled: 1 MB at least

3.2. Clock

3.2.1. High Frequency Clock

The high frequency clock on ESP8266EX is used to drive both transmit and receive mixers.

This clock is generated from internal crystal oscillator and external crystal. The crystal

frequency ranges from 24 MHz to 52 MHz.

The internal calibration inside the crystal oscillator ensures that a wide range of crystals can

be used, nevertheless the quality of the crystal is still a factor to consider to have

reasonable phase noise and good Wi-Fi sensitivity. Refer to Table 3-1 to measure the

frequency offset.

⚠ Notice:

SPI mode supported: Standard SPI, Dual SPI and Quad SPI. The correct SPI mode should be selected

when ﬂashing bin ﬁles to ESP8266. Otherwise, the downloaded ﬁrmware/program may not be working

properly.

Table 3-1. High Frequency Clock Speciﬁcations

Parameter

Symbol

Min

Max

Unit

Frequency

FXO

MHz

Loading capacitance

Motional capacitance

Series resistance

Frequency tolerance

ΔFXO

–15

ppm

Frequency vs temperature (–25°C ~ 75°C)

ΔFXO,Temp

–15

ppm

Espressif

$/$7 24

2018.09

3. Functional Description

3.2.2. External Clock Requirements

An externally generated clock is available with the frequency ranging from 24 MHz to 52

MHz. The following characteristics are expected to achieve good performance of radio.

3.3. Radio

ESP8266EX radio consists of the following blocks.

•2.4 GHz receiver

•2.4 GHz transmitter

•High speed clock generators and crystal oscillator

•Bias and regulators

•Power management

3.3.1. Channel Frequencies

The RF transceiver supports the following channels according to IEEE802.11b/g/n

standards.

Table 3-2. External Clock Reference

Parameter

Symbol

Min

Max

Unit

Clock amplitude

VXO

0.8

1.5

Vpp

External clock accuracy

ΔFXO,EXT

–15

ppm

Phase noise @1-kHz offset, 40-MHz clock

–120

dBc/Hz

Phase noise @10-kHz offset, 40-MHz clock

–130

dBc/Hz

Phase noise @100-kHz offset, 40-MHz clock

–138

dBc/Hz

Table 3-3. Frequency Channel

Channel No.

Frequency (MHz)

Channel No.

Frequency (MHz)

2412

2447

2417

2452

2422

2457

2427

2462

2432

2467

2437

2472

2442

2484

Espressif

$/$8 24

2018.09

3. Functional Description

3.3.2. 2.4 GHz Receiver

The 2.4 GHz receiver down-converts the RF signals to quadrature baseband signals and

converts them to the digital domain with 2 high resolution high speed ADCs. To adapt to

varying signal channel conditions, RF ﬁlters, automatic gain control (AGC), DC offset

cancelation circuits and baseband ﬁlters are integrated within ESP8266EX.

3.3.3. 2.4 GHz Transmitter

The 2.4 GHz transmitter up-converts the quadrature baseband signals to 2.4 GHz, and

drives the antenna with a high-power CMOS power ampliﬁer. The function of digital

calibration further improves the linearity of the power ampliﬁer, enabling a state of art

performance of delivering +19.5 dBm average TX power for 802.11b transmission and +18

dBm for 802.11n (MSC0) transmission.

Additional calibrations are integrated to offset any imperfections of the radio, such as:

•Carrier leakage

•I/Q phase matching

•Baseband nonlinearities

These built-in calibration functions reduce the product test time and make the test

equipment unnecessary.

3.3.4. Clock Generator

The clock generator generates quadrature 2.4 GHz clock signals for the receiver and

transmitter. All components of the clock generator are integrated on the chip, including all

inductors, varactors, loop ﬁlters, linear voltage regulators and dividers.

The clock generator has built-in calibration and self test circuits. Quadrature clock phases

and phase noise are optimized on-chip with patented calibration algorithms to ensure the

best performance of the receiver and transmitter.

3.4. Wi-Fi

ESP8266EX implements TCP/IP and full 802.11 b/g/n WLAN MAC protocol. It supports

Basic Service Set (BSS) STA and SoftAP operations under the Distributed Control Function

(DCF). Power management is handled with minimum host interaction to minimize active-

duty period.

3.4.1. Wi-Fi Radio and Baseband

The ESP8266EX Wi-Fi Radio and Baseband support the following features:

•802.11b and 802.11g

•802.11n MCS0-7 in 20 MHz bandwidth

•802.11n 0.4 μs guard-interval

•up to 72.2 Mbps of data rate

Espressif

$/$9 24

2018.09

3. Functional Description

•Receiving STBC 2x1

•Up to 20.5 dBm of transmitting power

•Adjustable transmitting power

•Antenna diversity

3.4.2. Wi-Fi MAC

The ESP8266EX Wi-Fi MAC applies low-level protocol functions automatically, as follows:

•2 × virtual Wi-Fi interfaces

•Infrastructure BSS Station mode/SoftAP mode/Promiscuous mode

•Request To Send (RTS), Clear To Send (CTS) and Immediate Block ACK

•Defragmentation

•CCMP (CBC-MAC, counter mode), TKIP (MIC, RC4), WEP (RC4) and CRC

•Automatic beacon monitoring (hardware TSF)

•Dual and single antenna Bluetooth co-existence support with optional simultaneous

receive (Wi-Fi/Bluetooth) capability

3.5. Power Management

ESP8266EX is designed with advanced power management technologies and intended for

mobile devices, wearable electronics and the Internet of Things applications.

The low-power architecture operates in the following modes:

•Active mode: The chip radio is powered on. The chip can receive, transmit, or listen.

•Modem-sleep mode: The CPU is operational. The Wi-Fi and radio are disabled.

•Light-sleep mode: The CPU and all peripherals are paused. Any wake-up events

(MAC, host, RTC timer, or external interrupts) will wake up the chip.

•Deep-sleep mode: Only the RTC is operational and all other part of the chip are

powered off.

Table 3-4. Power Consumption by Power Modes

Power Mode

Description

Power Consumption

Active (RF working)

Wi-Fi TX packet

Please refer to 5-2.

Wi-Fi RX packet

Moderm-sleep①

CPU is working

15 mA

Light-sleep②

0.9 mA

Deep-sleep③

Only RTC is working

20 uA

Shut down

0.5 uA

Espressif

$/$10 24

2018.09

3. Functional Description

📖 Notes:

①Modem-sleep mode is used in the applications that require the CPU to be working, as in PWM or

I2S applications. According to 802.11 standards (like U-APSD), it shuts down the Wi-Fi Modem

circuit while maintaining a Wi-Fi connection with no data transmission to optimize power

consumption. E.g. in DTIM3, maintaining a sleep of 300 ms with a wakeup of 3 ms cycle to receive

AP’s Beacon packages at interval requires about 15 mA current.

②During Light-sleep mode, the CPU may be suspended in applications like Wi-Fi switch. Without

data transmission, the Wi-Fi Modem circuit can be turned off and CPU suspended to save power

consumption according to the 802.11 standards (U-APSD). E.g. in DTIM3, maintaining a sleep of

300 ms with a wakeup of 3ms to receive AP’s Beacon packages at interval requires about 0.9 mA

current.

③During Deep-sleep mode, Wi-Fi is turned off. For applications with long time lags between data

transmission, e.g. a temperature sensor that detects the temperature every 100s, sleeps for 300s

and wakes up to connect to the AP (taking about 0.3 ~ 1s), the overall average current is less than

1mA. The current of 20 μA is acquired at the voltage of 2.5V.

Espressif

$/$11 24

2018.09

4. Peripheral Interface

4.1. General Purpose Input/Output Interface (GPIO)

ESP8266EX has 17 GPIO pins which can be assigned to various functions by programming

the appropriate registers.

Each GPIO PAD can be conﬁgured with internal pull-up or pull-down (XPD_DCDC can only

be conﬁgured with internal pull-down, other GPIO PAD can only be conﬁgured with internal

pull-up), or set to high impedance. When conﬁgured as an input, the data are stored in

software registers; the input can also be set to edge-trigger or level trigger CPU interrupts.

In short, the IO pads are bi-directional, non-inverting and tristate, which includes input and

output buffer with tristate control inputs.

These pins, when working as GPIOs, can be multiplexed with other functions such as I2C,

I2S, UART, PWM, and IR Remote Control, etc.

For low power operations, the GPIOs can also be set to hold their state. For instance, when

the IOs are not driven by internal and external circuits, all outputs will hold their states

before the chip entered the low power modes.

The required drive strength is small— 5 μA or more is enough to pull apart the latch.

4.2. Secure Digital Input/Output Interface (SDIO)

ESP8266EX has one Slave SDIO, the deﬁnitions of which are described as Table 4-1, which

supports 25 MHz SDIO v1.1 and 50 MHz SDIO v2.0, and 1 bit/4 bit SD mode and SPI

mode.

Table 4-1. Pin Deﬁnitions of SDIOs

Pin Name

Pin Num

Function Name

SDIO_CLK

IO6

SDIO_CLK

SDIO_DATA0

IO7

SDIO_DATA0

SDIO_DATA1

IO8

SDIO_DATA1

SDIO_DATA_2

IO9

SDIO_DATA_2

SDIO_DATA_3

IO10

SDIO_DATA_3

SDIO_CMD

IO11

SDIO_CMD

Espressif

$/$12 24

2018.09

4. Peripheral Interface

4.3. Serial Peripheral Interface (SPI/HSPI)

ESP8266EX has two SPIs.

•One general Slave/Master SPI

•One general Slave HSPI

Functions of all these pins can be implemented via hardware.

4.3.1. General SPI (Master/Slave)

4.3.2. HSPI (Slave)

Table 4-2. Pin Deﬁnitions of SPIs

Pin Name

Pin Num

Function Name

SDIO_CLK

IO6

SPICLK

SDIO_DATA0

IO7

SPIQ/MISO

SDIO_DATA1

IO8

SPID/MOSI

SDIO_DATA_2

IO9

SPIHD

SDIO_DATA_3

IO10

SPIWP

U0TXD

IO1

SPICS1

GPIO0

IO0

SPICS2

📖 Note:

SPI mode can be implemented via software programming. The clock frequency is 80 MHz at maximum

when working as a master, 20 MHz at maximum when working as a slave.

Table 4-3. Pin Deﬁnitions of HSPI (Slave)

Pin Name

Pin Num

Function Name

MTMS

IO14

HSPICLK

MTDI

IO12

HSPIQ/MISO

MTCK

IO13

HSPID/MOSI

MTDO

IO15

HPSICS

📖 Note:

SPI mode can be implemented via software programming. The clock frequency is 20 MHz at maximum.

Espressif

$/$13 24

2018.09

4. Peripheral Interface

4.4. I2C Interface

ESP8266EX has one I2C, which is realized via software programming, used to connect with

other microcontrollers and other peripheral equipments such as sensors. The pin deﬁnition

of I2C is as below.

Both I2C Master and I2C Slave are supported. I2C interface functionality can be realized via

software programming, and the clock frequency is 100 kHz at maximum.

4.5. I2S Interface

ESP8266EX has one I2S data input interface and one I2S data output interface, and

supports the linked list DMA. I2S interfaces are mainly used in applications such as data

collection, processing, and transmission of audio data, as well as the input and output of

serial data. For example, LED lights (WS2812 series) are supported. The pin deﬁnition of

I2S is shown in Table 4-5.

4.6. Universal Asynchronous Receiver Transmitter (UART)

ESP8266EX has two UART interfaces UART0 and UART1, the deﬁnitions are shown in

Table 4-6.

Table 4-4. Pin Deﬁnitions of I2C

Pin Name

Pin Num

Function Name

MTMS

IO14

I2C_SCL

GPIO2

IO2

I2C_SDA

Table 4-5. Pin Deﬁnitions of I2S

I2S Data Input

Pin Name

Pin Num

Function Name

MTDI

IO12

I2SI_DATA

MTCK

IO13

I2SI_BCK

MTMS

IO14

I2SI_WS

MTDO

IO15

I2SO_BCK

U0RXD

IO3

I2SO_DATA

GPIO2

IO2

I2SO_WS

Espressif

$/$14 24

2018.09

4. Peripheral Interface

Data transfers to/from UART interfaces can be implemented via hardware. The data

transmission speed via UART interfaces reaches 115200 x 40 (4.5 Mbps).

UART0 can be used for communication. It supports ﬂow control. Since UART1 features

only data transmit signal (TX), it is usually used for printing log.

4.7. Pulse-Width Modulation (PWM)

ESP8266EX has four PWM output interfaces. They can be extended by users themselves.

The pin deﬁnitions of the PWM interfaces are deﬁned as below.

The functionality of PWM interfaces can be implemented via software programming. For

example, in the LED smart light demo, the function of PWM is realized by interruption of the

timer, the minimum resolution reaches as high as 44 ns. PWM frequency range is

adjustable from 1000 μs to 10000 μs, i.e., between 100 Hz and 1 kHz. When the PWM

frequency is 1 kHz, the duty ratio will be 1/22727, and a resolution of over 14 bits will be

achieved at 1 kHz refresh rate.

Table 4-6. Pin Deﬁnitions of UART

Pin Type

Pin Name

Pin Num

Function Name

UART0

U0RXD

IO3

U0RXD

U0TXD

IO1

U0TXD

MTDO

IO15

U0RTS

MTCK

IO13

U0CTS

UART1

GPIO2

IO2

U1TXD

SD_D1

IO8

U1RXD

📖 Note:

By default, UART0 outputs some printed information when the device is powered on and booting up. The

baud rate of the printed information is relevant to the frequency of the external crystal oscillator. If the

frequency of the crystal oscillator is 40 MHz, then the baud rate for printing is 115200; if the frequency of

the crystal oscillator is 26 MHz, then the baud rate for printing is 74880. If the printed information exerts

any inﬂuence on the functionality of the device, it is suggested to block the printing during the power-on

period by changing (U0TXD, U0RXD) to (MTDO, MTCK).

Table 4-7. Pin Deﬁnitions of PWM

Pin Name

Pin Num

Function Name

MTDI

IO12

PWM0

MTDO

IO15

PWM1

MTMS

IO14

PWM2

GPIO4

IO4

PWM3

Espressif

$/$15 24

2018.09

4. Peripheral Interface

4.8. IR Remote Control

ESP8266EX currently supports one infrared remote control interface. For detailed pin

deﬁnitions, please see Table 4-8 below.

The functionality of Infrared remote control interface can be implemented via software

programming. NEC coding, modulation, and demodulation are supported by this interface.

The frequency of modulated carrier signal is 38 kHz, while the duty ratio of the square wave

is 1/3. The transmission range is around 1m which is determined by two factors: one is the

maximum current drive output, the other is internal current-limiting resistance value in the

infrared receiver. The larger the resistance value, the lower the current, so is the power, and

vice versa.

4.9. ADC (Analog-to-Digital Converter)

ESP8266EX is embedded with a 10-bit precision SAR ADC. TOUT (Pin6) is deﬁned as

below:

The following two measurements can be implemented using ADC (Pin6). However, they

cannot be implemented at the same time.

•Measure the power supply voltage of VDD3P3 (Pin3 and Pin4).

•Measure the input voltage of TOUT (Pin6).

Table 4-8. Pin Deﬁnitions of IR Remote Control

Pin Name

Pin Num

Function Name

MTMS

IO14

IR TX

GPIO5

IO 5

IR Rx

Table 4-9. Pin Deﬁnition of ADC

Pin Name

Pin Num

Function Name

TOUT

ADC Interface

Hardware Design

TOUT must be ﬂoating.

RF Initialization Parameter

The 107th byte of esp_init_data_default.bin (0 ~ 127 bytes), vdd33_const must

be set to 0xFF.

RF Calibration Process

Optimize the RF circuit conditions based on the testing results of VDD3P3 (Pin3

and Pin4).

User Programming

Use system_get_vdd33 instead of system_adc_read.

Hardware Design

The input voltage range is 0 to 1.0V when TOUT is connected to external circuit.

Espressif

$/$16 24

2018.09

4. Peripheral Interface

RF Initialization

Parameter

The value of the 107th byte of esp_init_data_default.bin (0 ~ 127 bytes),

vdd33_const must be set to the real power supply voltage of Pin3 and Pin4.

The unit and effective value range of vdd33_const is 0.1V and 18 to 36,

respectively, thus making the working power voltage range of ESP8266EX

between 1.8V and 3.6V,

RF Calibration Process

Optimize the RF circuit conditions based on the value of vdd33_const. The

permissible error is ±0.2V.

User Programming

Use system_adc_read󰲧instead of system_get_vdd33.

📖 Notes:

esp_init_data_default.bin is provided in SDK package which contains RF initialization parameters (0 ~

127 bytes). The name of the 107th byte in esp_init_data_default.bin is vdd33_const, which is deﬁned as

below:

•When vdd33_const = 0xff, the power voltage of Pin3 and Pin4 will be tested by the internal self-

calibration process of ESP8266EX itself. RF circuit conditions should be optimized according to the

testing results.

•When 18 =< vdd33_const =< 36, ESP8266EX RF Calibration and optimization process is implemented

via (vdd33_const/10).

•When vdd33_const < 18 or 36 < vdd33_const < 255, vdd33_const is invalid. ESP8266EX RF

Calibration and optimization process is implemented via the default value 3.3V.

Espressif

$/$17 24

2018.09

5. Electrical Speciﬁcations

5.1. Electrical Characteristics

5.2. RF Power Consumption

Unless otherwise speciﬁed, the power consumption measurements are taken with a 3.0V

supply at 25°C of ambient temperature. All transmitters’ measurements are based on a

50% duty cycle.

Table 5-1. Electrical Characteristics

Parameters

Conditions

Min

Typical

Max

Unit

Operating Temperature Range

–40

Normal

125

℃

Maximum Soldering Temperature

IPC/JEDEC J-

STD-020

260

℃

Working Voltage Value

2.5

3.3

3.6

I/O

VIL

–0.3

0.25VIO

VIH

0.75VIO

3.6

VOL

0.1VIO

VOH

0.8VIO

IMAX

Electrostatic Discharge (HBM)

TAMB=25℃

Electrostatic Discharge (CDM)

TAMB=25℃

0.5

Table 5-2. Power Consumption

Parameters

Min

Typical

Max

Unit

TX 802.11b, CCK 11Mbps, POUT=+17 dBm

170

TX 802.11g, OFDM 54Mbps, POUT=+15 dBm

140

TX 802.11n, MCS7, POUT=+13dBm

120

Rx 802.11b, 1024 bytes packet length , –80 dBm

Rx 802.11g, 1024 bytes packet length, –70 dBm

Rx 802.11n, 1024 bytes packet length, –65 dBm

Espressif

$/$18 24

2018.09

5. Electrical Speciﬁcations

5.3. Wi-Fi Radio Characteristics

The following data are from tests conducted at room temperature, with a 3.3V power

supply.

Table 5-3. Wi-Fi Radio Characteristics

Parameters

Min

Typical

Max

Unit

Input frequency

2412

2484

MHz

Output impedance

39+j6

Output power of PA for 72.2 Mbps

15.5

16.5

17.5

dBm

Output power of PA for 11b mode

19.5

20.5

21.5

dBm

Sensitivity

DSSS, 1 Mbps

–98

dBm

CCK, 11 Mbps

–91

dBm

6 Mbps (1/2 BPSK)

–93

dBm

54 Mbps (3/4 64-QAM)

–75

dBm

HT20, MCS7 (65 Mbps, 72.2 Mbps)

–72

dBm

Adjacent Channel Rejection

OFDM, 6 Mbps

OFDM, 54 Mbps

HT20, MCS0

HT20, MCS7

Espressif

$/$19 24

2018.09

6. Package Information

Figure 6-1. ESP8266EX Package

Espressif

$/$20 24

2018.09

Appendix Ⅰ

I. Appendix - Pin List

For detailed pin information, please see ESP8266 Pin List.

•Digital Die Pin List

•Buffer Sheet

•Register List

•Strapping List

📖 Notes:

•INST_NAME refers to the IO_MUX REGISTER deﬁned in eagle_soc.h, for example MTDI_U refers to

PERIPHS_IO_MUX_MTDI_U.

•Net Name refers to the pin name in schematic.

•Function refers to the multifunction of each pin pad.

•Function number 1 ~ 5 correspond to FUNCTION 0 ~ 4 in SDK. For example, set MTDI to GPIO12 as

follows.

- #define󰲧FUNC_GPIO12󰲧󰲧3󰲧//defined󰲧in󰲧eagle_soc.h

- PIN_FUNC_SELECT(PERIPHS_IO_MUX_MTDI_U,FUNC_GPIO12)

Espressif

$/$21 24

2018.09

Appendix Ⅱ

II. Appendix - Learning

Resources

II.1. Must-Read Documents

•ESP8266 Quick Start Guide

Description: This document is a quick user guide to getting started with ESP8266. It

includes an introduction to the ESP-LAUNCHER, instructions on how to download

ﬁrmware to the board and run it, how to compile the AT application, as well as the

structure and debugging method of RTOS SDK. Basic documentation and other related

resources for the ESP8266 are also provided.

•ESP8266 SDK Getting Started Guide

Description: This document takes ESP-LAUNCHER and ESP-WROOM-02 as examples

of how to use the ESP8266 SDK. The contents include preparations before compilation,

SDK compilation and ﬁrmware download.

•ESP8266 Pin List

Description: This link directs you to a list containing the type and function of every

ESP8266 pin.

•ESP8266 Hardware Design Guideline

Description: This document provides a technical description of the ESP8266 series of

products, including ESP8266EX, ESP-LAUNCHER and ESP-WROOM.

•ESP8266 Hardware Matching Guide

Description: This document introduces the frequency offset tuning and antenna

impedance matching for ESP8266 in order to achieve optimal RF performance.

•ESP8266 Technical Reference

Description: This document provides an introduction to the interfaces integrated on

ESP8266. Functional overview, parameter conﬁguration, function description,

application demos and other pieces of information are included.

•ESP8266 Hardware Resources

Description: This zip package includes manufacturing BOMs, schematics and PCB

layouts of ESP8266 boards and modules.

•FAQ

II.2. Must-Have Resources

•ESP8266 SDKs

Espressif

$/$22 24

2018.09

Appendix Ⅱ

Description: This webpage provides links both to the latest version of the ESP8266 SDK

and the older ones.

•ESP8266 Tools

Description: This webpage provides links to both the ESP8266 ﬂash download tools and

the ESP8266 performance evaluation tools.

•ESP8266 Apps

•ESP8266 Certiﬁcation and Test Guide

•ESP8266 BBS

•ESP8266 Resources!

Espressif

$/$23 24

2018.09

Disclaimer and Copyright Notice

Information in this document, including URL references, is subject to change without

notice.

THIS DOCUMENT IS PROVIDED AS IS WITH NO WARRANTIES WHATSOEVER,

INCLUDING ANY WARRANTY OF MERCHANTABILITY, NON-INFRINGEMENT, FITNESS

FOR ANY PARTICULAR PURPOSE, OR ANY WARRANTY OTHERWISE ARISING OUT

OF ANY PROPOSAL, SPECIFICATION OR SAMPLE.

All liability, including liability for infringement of any proprietary rights, relating to use of

information in this document is disclaimed. No licenses express or implied, by estoppel or

otherwise, to any intellectual property rights are granted herein.

The Wi-Fi Alliance Member logo is a trademark of the Wi-Fi Alliance. The Bluetooth logo is

a registered trademark of Bluetooth SIG.

All trade names, trademarks and registered trademarks mentioned in this document are

property of their respective owners, and are hereby acknowledged.

Espressif IOT Team"

www.espressif.com

