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UART Protocol for Zigbee Three-level Architecture

Last Updated on : 2021-06-07 06:30:25download

Overview

Tuya universal asynchronous receiver/transmitter (UART) protocol applies to the three-level architecture of Tuya Zigbee modules, the MCU, and terminal devices. It is used for the serial communication between the Tuya Zigbee modules and the directly-connected MCU repeaters. Terminal devices can be connected with repeaters through the wired mode. The architecture diagram is shown below.

UART Protocol for Zigbee Three-level Architecture

Hardware connection

Tuya Zigbee modules and MCU master control are both powered by DC 3.3V.

The UART communication Baud between Tuya Zigbee module and the MCU is set to 115200-8-N-1, and there is no data flow control. The UART interface pins use standard logic. In the idle status, the TXD and RXD pins are both high level, with the low level as the start bit and the high level as the stop bit. Even if the device enters sleep status, the pin remains at a high level.

Serial communication

Frame format

The UART communication data frame between Tuya Zigbee module and the MCU is composed of the frame header (Front), version (Ver), command (Cmd), data length (Length), data (Data), and checksum (Check). The definition and description are as follows.

Octets: 2 1 2 1 2 Variable 1
Front Ver Seq Cmd Length Data Check

Frame format description

Field Description
Header (Front) 2-byte leader character, fixed as 0x55aa
Version (Ver) Serial communication protocol version for upgrade and extension
Sequence (Seq) Transmission data serial number, ranging from 1 to 0xfff0, while other serial numbers are reserved for special functions
Command (Cmd) For specific frame type, see the next table
Data length (Length) The valid data length transmitted. The data length of a single frame does not exceed 100 bytes
Data (Data) Valid data transmitted
Checksum (Check) Data check. Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Commands are described as follows:

Cmd ID Description
0x01 Query and report the product information
0x02 Query and report the device status
0x03 Reset the Zigbee device
0x04 The terminal device sends an adding request
0x05 The terminal device sends an adding request
0x06 RF test
0x07 Notify the MCU to synchronize data
0x08 Send a control command
0x09 Report the device status
0x0B Query the version
0x0c OTA notification
0x0D OTA request
0x0E OTA completion notification
0x0C—0x23 Reserved
0x24 Time synchronization
  • All data greater than one byte shall be transmitted in big-endian mode.

  • Generally, one command is sent by one party and received by the other party in a synchronous way. That is, one party sends the command, and the other party responds. If the sender does not receive the correct response packet within the specified time period, the transmission times out, as shown in the following figure:

    UART Protocol for Zigbee Three-level Architecture

    Note: For specific communication modes, see the section Protocol details.

  • Sending module control commands and reporting MCU status works in an asynchronous way. Assuming that the control command of the module is x, and the command of MCU status reported is y, the data transmission is as follows.
    Send the module control command:

    UART Protocol for Zigbee Three-level Architecture

    Report the MCU status:

    To report the MCU status, the module sends data commands to the MCU, and the MCU returns the status after execution.

    UART Protocol for Zigbee Three-level Architecture

Protocol details

Query product information of MCU

Product information consists of the product ID and MCU software version.

  • Product ID (PID) is generated in the Tuya IoT Platform to record product information in the cloud.

  • MCU software version number is in the dot-decimal format X.X.X, in which X is a decimal number. The actual MCU version is represented by one byte, and the bit allocation is xx.xx.xxxx. That is, the highest version that can be represented is 3.3.15.

For example, the module sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x01
Data length 2 0x0000
Data 0 None
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

For example, 0x55aa 02 N 01 0000 xx.

The MCU returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x01
Data length 2 N
Data N {“p”:”AIp08kLI”, “v”:”1.0.0” }
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

For example, {“p”:” AIp08kLI”,“v”:”2.0.0” }.

p represents the product ID, which is AIp08kLI.

v represents the MCU version number, which is 2.0.0.

0x55aa 02 N 01 00 1c 7b2270223a2241497031386b4c49222c2276223a22312e302e30227d xx

Report network status of the Zigbee module

Device status ID Description
0x00 The device is not connected to the gateway
0x01 The device is connected to the gateway
0x02 The device network status has an exception
0x03 The device is in the pairing status
  • The device is not connected to the network: The device is powered on for the first time, fails to connect to the network, or is off the network. The status is sent to the MCU.

  • The device is connected to the network: The device is successfully connected to the network. The status is sent to the MCU.

  • When the module restarts or the power supply is cut off and then connected again, the module network status is actively sent to the MCU.

  • When the network status of the module changes, the module network status is actively sent to the MCU.

For example, the module sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x02
Data length 2 0x0001
Data 1 Indicate the working status of the module: 0x00: status 1 and 0x01: status 2
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

For example, 0x55aa 02 N 02 0001 00 xx.

The MCU returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x02
Data length 2 0x0000
Data 0 None
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

For example, 0x55aa 02 N 02 0000 xx.

Configure the Zigbee module

There are two types of commands to configure the Zigbee module.

Note: After the MCU sends the network pairing command, the module will clear previous sub-devices. You need to re-add the sub-devices after successful network pairing.

Command Description
0x00 Reset the module software
0x01 Configure the module to start pairing (disconnect and then pair again).

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x03
Data length 2 0x0001
Data 0 0x00/0x01
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

For example, 0x55aa 02 N 03 0001 01 xx.

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x03
Data length 2 0x0000
Data 0 None
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

For example, 0x55aa 02 N 03 0000 xx.

The terminal device sends an adding request

This command is used when the MCU registers the terminal device with the Zigbee gateway.

Note: This command shall be sent after the module is successfully paired.

After the MCU sends the network pairing command, the module will clear the previous sub-devices. You need to re-add the sub-devices after successful network pairing.

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x04
Data length 2 The length of actually transmitted data
The number of devices 1 The number (N) of devices is ≤10. No more than 10 devices can be registered in a single batch. If there are more than 10 devices, the data can be sent in two frames.
PID of the terminal device 1 8 Device manufacturer number provided by Tuya
Address of the device 1 2 Actual address of the device
PID of the terminal device 2 8 Device manufacturer number provided by Tuya
Address of the device 2 2 Actual address of the device
PID of the terminal device N 8 Device manufacturer number provided by Tuya
Address of the device N 2 Actual address of the device
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x04
Data length 2 0x0000
Data 0 None
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The terminal device sends an adding request (extension)

This command is used when the MCU registers the terminal device with the Zigbee gateway.

Note: This command shall be sent after the module is successfully paired.

This protocol is for an extension. If the PID length exceeds 8 bytes, this command must be used.

The sub-device address is 2 bytes by default, and the Zigbee gateway will treat the address as a number. Therefore, even for devices with different PIDs, the address must be unique in the same Zigbee gateway.

After the MCU sends the network pairing command, the module will clear the previous sub-devices. You need to re-add the sub-devices after successful network pairing.

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x05
Data length 2 Data length
PID length To be determined PID length
PID To be determined The product ID
The number of sub-devices 1 The number of sub-devices (M)
Sub-device address 2*M Registered sub-device addresses are arranged in order
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x05
Data length 2 0x0000
Data 0 None
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Functional test of Zigbee devices

Scan the RSSI value of the specified channel, and return the scan result and signal strength percentage. This command can work properly only when the device is not paired, and the module must be restarted after a single test is completed.

When the channel is channel No. 11 to 26, channel No. 11 is used by default.

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x06
Data length 2 0x0001
Data Data Channel value (11–26)
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x06
Data length 2 0x0002
Data 2 Data length has 2 bytes. Data[0]: 0x00 means failure, and 0x01 means success. When Data[0] is 0x01, which means success, Data[1] is signal strength (0-100, 0: the weakest signal, and 100: the strongest signal). When Data[0] is 0x00, which means failure, if Data[1] is 0x00, the RSSI is not found in the specified channel. If Data[1] is 0x01, the module has not generated an authorization key.
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The valid channel value is 11 to 26. In case of an invalid channel, channel No. 11 will be used.

Notify the MCU to synchronize sub-device status

This notification will be sent after successful pairing.

This notification will also be sent after the gateway is powered off and then powered on again.

After receiving this command, MCU shall report the status of the sub-device. The length of the reported data cannot exceed 62 bytes. Otherwise, the data shall be reported in multiple packets.

For example, Zigbee sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x07
Data length 2 0x0000
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x07
Data length 2 0x0000
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Send a control command

The format of the command sending frame is as follows:

Octets: 2 1 1 1 2 2 Variable 1
Front Ver Seq Cmd Date Length Address Check
Octets: Variable Variable Variable Variable
CmdData Unit-1 CmdData Unit-2 CmdData Unit-3 CmdData Unit-n
Octets: 1 1 2 Variable
Dpid Type Len Value
  • Data point command and status data unit is shown as follows:
Data segment Length (byte) Description
Dpid 1 Data point serial number
Type 1 The specific data type of a data point on the IoT Platform, which is marked with the following “Value”.
Type Value Length (byte) Description
raw 0x00 N Corresponding to the raw data point (module pass-through)
bool 0x01 1 Value range: 0x00 and 0x01
value 0x02 4 Corresponding to the integer type, which is expressed in big-endian
string 0x03 N Corresponding to a specific string
enum 0x04 1 Enumeration type, ranging from 0 to 255
bitmap 0x05 1/2/4 Express in big-endian in case of more than 1 byte
Len 2 The length corresponds to the number of bytes of the value
Value 1/2/4/N Express with hex, and adopt big-endian transmission in case of more than 1 byte
  • For the data point command/status data unit, except the “raw” type, all other types belong to the “obj” type data point.

  • “Command sending” can contain “command data units” of multiple “obj” data points.

  • Command sending is an asynchronous processing protocol, corresponding to the data point status reporting of the MCU.

For example, the module sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x08
Data length 2 It depends on the type and number of the command data unit and sub-device address length.
Sub-device address 2 Actual address of the device
Data N See the section Command data unit
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The MCU returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x08
Data length 1 0x0003
Sub-device address 2 Actual address of the device
Data 1 0x00: success, 0x01: failure
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Report the device status

  • After the MCU receives the command sent by the module and executes the corresponding action, the MCU shall passively report the new status to the module.

After the status is executed correctly, only the data point status of the executed operation is reported.

  • Status reporting is processed in a synchronous manner. The module will immediately return an ACK to the MCU after receiving a message from the data point.

  • Status reporting can contain command data units of multiple data points.

  • The maximum length of the DP data is 59 bytes.

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x09
Data length 2 It depends on the type and number of the status data unit and sub-device address length.
Sub-device address 2 Actual address of the device
Data N See the section Status data unit
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x09
Data length 2 0x0003
Sub-device address 2 Actual address of the device
Data 0 0x00: The status is reported successfully, 0x01: Failed to report the status
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Query MCU version

To support the MCU update, this command must be implemented, and it can also be actively reported by the MCU.

  • Query MCU version: 1. During pairing. 2. An exception occurred during the MCU update.

  • Active reporting MCU version: 1. After successful pairing (adding is required). 2. The update ends.

  • Version format: The maximum version that can be represented is 3.3.15. The version is represented by one byte, that is, xx.xx.xxxx. But the gateway will not recognize the version information. The version information can be entered at will in the background, so the version data used by the MCU cannot exceed 3.3.15.

For example, the module sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 Generated by the module
Command 1 0x0B
Data length 2 0x0000
Data 0
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The MCU responds or the module sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 Seq sent by the MCU
Command 1 0x0B
Data length 2 0x0001
Data 1 Current version number: 01.00.0001 represents 1.0.1
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

OTA updates notification

For example, the module sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 Generated by the module
Command 1 0x0c
Data length 2 0x0011
Data 8 Data[0]–Data[7] PID
Data 1 Version number after update: 01.00.0001 represents 1.0.1
Data 4 Firmware size up to 256 KB
Data 4 Firmware checksum: Start from the first byte of the firmware, add up all the bytes, and then divide the sum by 2^32 to get the remainder
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The MCU responds to the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 Seq sent by the module
Command 1 0x0c
Data length 2 0x0001
Data 1 0x00: OK and 0x01: error
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Request OTA firmware content

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 0x0000
Command 1 0x0D
Data length 2 0x000c
Data 8 PID
Data 1 Version number after update: 01.00.0001 represents 1.0.1
Data 4 The offset of the data packet (location of the firmware)
Data 1 Packet size
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module responds:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 0x0000
Command 1 0x0D
Data length 2 0x000e+N
Data 1 Status: 0 means success. 1 means failure.
Data 8 PID
Data 1 Version number after update: 01.00.0001 represents 1.0.1
Data 4 The offset of the data packet (location of the firmware)
Data N Data
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Report OTA firmware update result

This result shall be reported after the MCU update is completed. Regardless of the MCU update result, as long as the update is initiated, the update process must be terminated by the result reporting command.

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 Seq sent by the MCU
Command 1 0x0E
Data length 2 0x000a
Data 1 Status: 0 means success. 1 means failure.
Data 8 PID
Data 1 Version number after update: 01.00.0001 represents 1.0.1
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module responds:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Sequence (Seq) 2 Seq sent by the MCU
Command 1 0x0E
Data length 2 0x0001
Data 1 0x00: OK and 0x01: error
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

Time synchronization

Time synchronization is used for the MCU to test the network time that is synchronized with the gateway.

MCU sends the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x24
Data length 2 0x0000
Data Data NA
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The module returns the following command:

Field Length (byte) Description
Header 2 0x55aa
Version 1 0x02
Serial number 2 N
Command 1 0x024
Data length 2 0x0002
Data 2 The time value has 8 bytes. For more information about the format, see the following time synchronization data format.
Checksum 1 Start from the header, add up all the bytes, and then divide the sum by 256 to get the remainder

The data format of time synchronization includes a standard timestamp and a local timestamp.

Variable Variable
Standard timestamp (4 bytes) Local timestamp (4 bytes)

Data format of time synchronization

The standard timestamp is the total seconds from GMT 00:00:00, January 1, 1970 to the current time.

Local timestamp = standard timestamp + the difference in seconds between standard time and local time (including time zone and daylight saving time).