The Complete Handbook of AT Commands

AT commands, short for Attention commands, are a set of instructions used to control modems. These commands originated from the Hayes command set and have become essential for IoT (Internet of Things) devices, especially for managing WiFi modules. They allow users to perform functions such as connecting to a network, sending data, and configuring device settings, making them crucial for IoT applications.

The structure of AT commands is straightforward. Each command starts with the prefix AT (for Attention) followed by the specific instruction. These commands can be sent through a terminal program or software that communicates with the WiFi module. They are not limited to basic tasks; advanced commands can configure security settings, manage power modes, and handle data transmission.

AT Commands structure

In the IoT field, WiFi modules like the ESP8266 and ESP32 are popular for their low cost and flexibility. These modules use AT commands to perform a wide range of functions. This makes AT commands a powerful tool for IoT developers, enabling efficient and effective device management and communication.

Each instruction can have four types of AT commands.

Each AT command should end with "\\r\\n" and string values must be enclosed in double quotation marks. Note that not all AT commands include the four options.

AT Commands cheat sheet

This documentation covers the AT command instruction set and its usage. The instruction set is divided into the following categories: basic AT commands, WiFi function AT commands, and TCP/IP AT commands.

Below is detailed information on each command, including usage instructions and possible responses.

Basic AT Commands

This section provides an explanation of fundamental AT commands, detailing their essential functions and usage instructions.

AT

This command is used to verify that the AT command interface is operational. When executed, the device should respond with "OK" if it is functioning correctly.

AT+RST

This command restarts the module. It is useful for rebooting the device to apply new settings or recover from an error state.

AT+GMR

This command displays the firmware version of the module. It is helpful for checking the current version and ensuring compatibility with other software.

Parameters:

• <number>: version Info, length: 8bytes

AT+GSLP

This command puts the module into deep-sleep mode to conserve power. It is particularly useful for battery-operated IoT devices that need to minimize power consumption.

Parameters:

• <time>: set the sleep time in ms. Module will wake up after provided ms in deep-sleep.

ATE

This command controls whether the characters received by the module are echoed back to the terminal. This can be useful for debugging and command verification.

Parameters:

• ATE0: disable echo.

• ATE1: enable echo.

WiFi AT Commands

This section presents AT commands specifically designed for managing WiFi functionality. It describes their functions and provides instructions on how to use them effectively.

AT+CWMODE

This command sets the operating mode of the WiFi module. It can be configured to operate as a station, connecting to an existing network, a softAP, creating its own access point, or both simultaneously.

Parameters:

• <mode>: WiFi mode

  • 1 - station mode

  • 2 - access point mode

  • 3 - access point + station mode

AT+CWJAP

This command is used to connect the device to a specific access point (AP). It requires the SSID (network name) and password of the target AP to establish a connection.

Parameters:

• <ssid>: service set identifier

• <pwd>: access password (max 64 bytes)

AT+CWLAP

This command retrieves a list of available access points in the vicinity. It provides information such as the SSID, signal strength, and security type of each detected AP.

Parameters:

• <enc>: encryption

  • 0 - OPEN

  • 1 - WEP

  • 2 - WPA_PSK

  • 3 - WPA2_PSK

  • 4 - WPA_WPA2_PSK

• <ssid>: service set identifier

• <rssi>: signal strength

• <mac>: MAC address

AT+CWQAP

This command disconnects the device from the currently connected access point.

AT+CWSAP

When operating in softAP mode, this command configures parameters such as the SSID, password, and channel of the access point being created.

Parameters:

• <ssid>: service set identifier

• <pwd>: access password (max 64 bytes)

• <chl>: channel ID

• <enc>: encryption

  • 0 - OPEN

  • 1 - WEP

  • 2 - WPA_PSK

  • 3 - WPA2_PSK

  • 4 - WPA_WPA2_PSK

AT+CWLIF

This command retrieves the IP addresses of devices currently connected to the WiFi module acting as a softAP.

Parameters:

• <ip>: IP address of stations which are connected to the soft AP

AT+CWDHCP

This command controls whether the module assigns IP addresses dynamically using DHCP (Dynamic Host Configuration Protocol). It can be used to enable or disable DHCP functionality.

Parameters:

• <mode>: WiFi mode

  • 0 - set softAP

  • 1 - set station

  • 2 - set both softAP and station

• <en>: DHCP status

  • 0 - Enable DHCP

  • 1 - Disable DHCP

AT+CIPSTAMAC

This command allows the user to manually set the MAC address of the WiFi module when operating in station mode.

Parameters:

• <mac>: MAC address

AT+CIPAPMAC

This command allows the user to manually set the MAC address of the WiFi module when operating in softAP mode.

Parameters:

• <mac>: MAC address

AT+CIPSTA

This command configures the IP address of the WiFi module when operating in station mode.

Parameters:

• <ip>: IP address

AT+CIPAP

This command configures the IP address of the WiFi module when operating in station mode.

Parameters:

• <ip>: IP address

TCP/IP AT Commands

This section covers AT commands related to TCP/IP communication. It outlines their functions and offers guidance on usage.

AT+CIPSTATUS

This command retrieves the current status of the connection, indicating whether it is idle, connected, or in the process of establishing a connection.

Parameters:

• <status>: connection status

  • 2: got IP

  • 3: connected

  • 4: disconnected

• <id>: id of the connection (0~4), for multi-connect

• <type>: TCP or UDP

• <ip> IP address

• <port>: port number

• <mode>: connection mode

  • 0: running as client

  • 1: running as server

AT+CIPSTART

This command is used to initiate a TCP connection with a remote server or register a UDP port for communication.

Single connection (+CIPMUX=0):

Multiple connections (+CIPMUX=1):

Note: <mode> can only be used when <localport> is set.

Parameters:

• <id>: id of the connection (0~4), for multi-connect

• <type>: TCP or UDP

• <ip> remote IP address

• <port> remote port

• <localport> local port for UDP connections only

• <mode> connection mode for UDP connections only

  • 0 - destination peer entity of UDP will not change.

  • 1 - destination peer entity of UDP can change once.

  • 2 - destination peer entity of UDP is allowed to change.

AT+CIPSEND

This command is used to send data over an established TCP or UDP connection. It allows users to transmit information to remote servers or other devices.

Parameters:

• <id>: id of the connection (0~4), for multi-connect

• <length>: data length (max 2048 bytes)

AT+CIPCLOSE

This command terminates an active TCP or UDP connection, freeing up resources and ending communication with the remote server or device.

When connection id 5 is provided, all connections will be closed.

Parameters:

• <id>: id of the connection (0~4), for multi-connect

AT+CIFSR

This command retrieves the local IP address assigned to the module, allowing users to identify the device on the network.

Parameters:

• <ip> IP address

AT+CIPMUX

This command configures the module to support multiple simultaneous connections, enabling it to handle multiple clients or connections concurrently.

This mode can only be changed after all connections are disconnected. If server is started, reboot is required.

Parameters:

• <mode>: connection mode

  • 0 - single connection

  • 1 - multiple connections

AT+CIPSERVER

This command sets up the module as a server, allowing it to accept incoming connections from clients and respond to requests.

Note:

1. Server can only be created when AT+CIPMUX=1

2. Server monitor will automatically be created when Server is created.

3. When a client is connected to the server, it will take up one connection ID.

Parameters:

• <mode>: server action

  • 0 - delete server (need to follow by restart)

  • 1 - create server

• <port>: port number, default is 333

AT+CIPMODE

This command configures the transmission mode of the module, allowing users to choose between transparent and non-transparent modes for data communication.

Parameters:

• <mode>: transmission mode

  • 0 - normal

  • 1 - unvarnished

AT+CIPSTO

This command sets the timeout duration for connections when the module is operating as a TCP server. It helps manage connection durations and resource usage effectively.

Parameters:

• <time>: server timeout, range 0-7200 seconds

+IPD

When network data is received, the module will send the data through the serial port using the +IPD command.

Parameters:

• <id>: id of the connection (0~4), for multi-connect

• <length>: data length

• <data>: data received

Conclusion

AT commands are important for the operation of IoT devices, particularly those with WiFi modules. Their straightforwardness and efficiency make them indispensable for connecting devices, configuring settings, and managing data transmission. Mastering AT commands can significantly enhance the performance and control of IoT systems, highlighting their key contribution to the advancement of smart, connected technologies.