Chain Angle UART Control Protocol (Documentation V1)

1. Basic Information

Item	Description
Communication method	UART / serial port asynchronous communication
Device	Chain Angle
SKU	U208
Baud Rate	115200 bps
Data Bits	8 bit
Stop bit	1 bit
Parity	None
Flow Control	None
Document version	V1

2. Data Frame Format

All packets start with 0xAA 0x55 and end with 0x55 0xAA. Multi-byte length fields are entered low byte first.

2.1 Request Frame Format

Field	length	Description
Header	2	Fixed to `0xAA 0x55`
Length	2	Number of bytes from `Index` to `CRC`, low byte first
Index	1	The index ID of the device in the Chain link
Cmd	1	request command code
Req Data	n	Request parameters; if there are no parameters, the length is `0`
CRC	1	See "3. Verification Instructions"
Tail	2	Fixed to `0x55 0xAA`

Request Frame:
  AA 55 <Length_low> <Length_high> <Index> <Cmd> <Req Data...> <CRC> 55 AA

2.2 Response Frame Format

Field	length	Description
Header	2	Fixed to `0xAA 0x55`
Length	2	Number of bytes from `Index` to `CRC`, low byte first
Index	1	The index ID of the device in the Chain link
Cmd	1	Consistent with request `Cmd`
Resp Data	n	Response data, the structure is defined by the corresponding command
CRC	1	See "3. Verification Instructions"
Tail	2	Fixed to `0x55 0xAA`

Response Frame:
  AA 55 <Length_low> <Length_high> <Index> <Cmd> <Resp Data...> <CRC> 55 AA

2.3 Response Data Convention

situation	response rules
Reply with status code	`Operation_status = 0` means the operation failed, `Operation_status = 1` means the operation was successful
Reply without status code	The judgment method of success or failure shall be based on the "Notes" of the corresponding instruction.

3. Checksum

Item	rules
Check field	`CRC`
Checksum range	Starting from `Index`, accumulate to the last byte of `Data`
Checksum algorithm	Excluding the packet header, packet trailer, Length and CRC, the remaining bytes are accumulated and the lower 8-bits are taken.
Empty Data	`CRC = (Index + Cmd) & 0xFF`
Checksum failure	discard the frame

CRC = (Index + Cmd + Data[0] + ... + Data[n]) & 0xFF

3.1 Checksum Example

#include <stddef.h>
#include <stdint.h>

uint8_t chain_calc_crc(uint8_t index, uint8_t cmd,
                       const uint8_t *data, size_t data_len)
{
    uint16_t sum = index + cmd;

    for (size_t i = 0; i < data_len; i++) {
        sum += data[i];
    }

    return (uint8_t)(sum & 0xFF);
} 

4. Quick overview of commands

Cmd	Command name	Request Length	Reply Length	Request clarification	Response description	Details
`0x20`	Set RGB values	`0x0005+Num*3`	`0x0004`	Index_id (device index ID), Index (starting coordinates of the RGB lamp), Num (number of RGB to be set), RGB value	Operation_status	`5.1`
`0x21`	Get RGB value	`0x0005`	`0x0004+Num*3/0x04`	Index_id (device index ID), Index (starting coordinates of RGB lights), Num (number of RGB lights to be read)	RGB value	`5.2`
`0x22`	Set RGB light brightness	`0x0005`	`0x0004`	Index_id (device index ID), Light (RGB brightness, 0~100, default 40), Save_to_flash (whether to save to internal Flash)	Operation_status	`5.3`
`0x23`	Get RGB light brightness	`0x0003`	`0x0004`	Index_id (device index ID)	Light (RGB brightness)	`5.4`
`0x30`	Read Angle's 12-bit ADC	`0x0003`	`0x0005`	Index_id (device index ID)	ADC value	`5.5`
`0x31`	Read Angle's 8-bit ADC	`0x0003`	`0x0004`	Index_id (device index ID)	ADC value	`5.6`
`0x32`	Set the rotation control state to determine whether the encoder value increases or decreases when rotating clockwise	`0x0005`	`0x0004`	Index_id (device index ID), Clockwise_direct (clockwise status direction), Save_to_flash (whether to save the configuration to internal Flash)	Operation_status	`5.7`
`0x33`	Get rotation control status	`0x0003`	`0x0004`	Index_id (device index ID)	Clockwise_direct value	`5.8`
`0xF8`	Query device unique UID	`0x0004`	`0x0004+4/12`	Index_id (device index ID), UID_Type	Operation_status、UID	`5.9`
`0xF9`	Query the upgrade program version number	`0x0003`	`0x0004`	Index_id (device index ID)	Bootloader_version	`5.10`
`0xFA`	Query the device software version number	`0x0003`	`0x0004`	Index_id (device index ID)	Firmware_version	`5.11`
`0xFB`	Query device type	`0x0003`	`0x0005`	Index_id (device index ID)	Device_type	`5.12`
`0xFC`	Enumeration request, sent by the chain link change end device, and when the device is powered on, notifying the host to update the link device status	`Device-initiated report`	`Device-initiated report`	none	none	`5.13`
`0xFD`	Heartbeat packets, regular communication between chain devices, can self-discover whether they are end devices, and the host can also use heartbeat packets to determine whether there is a chain device connected.	`0x0003`	`0x0003`	none	none	`5.14`
`0xFE`	Users can obtain the number of link devices through enumeration	`0x0004`	`0x0004`	Send_num (default 0, used to record the number of devices)	Receive_num (the value represents the number of devices)	`5.15`

5. Command Details

5.1 Set RGB value - `Cmd 0x20`

Request data

Input parameters: Index_id (device index ID), Index (starting coordinates of the RGB lamp), Num (number of RGB to be set), RGB value

Request Frame:
  AA 55 | 0x05+Num*3 | 0x00 | Index_id | 0x20 | Index | Num | R | G | B | ... | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x20 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation successful
Index is the starting coordinate of the RGB light, starting from 0. The Angle device has only one RGB light, so Index = 0, Num = 1

5.2 Get RGB value - `Cmd 0x21`

Request data

Input parameters: Index_id (device index ID), Index (starting coordinates of RGB lights), Num (number of RGB lights to be read)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x21 | Index | Num | CRC | 55 AA

Response Data

Return parameter: RGB value

Response Frame:
  AA 55 | 0x04+Num*3/0x04 | 0x00 | Index_id | 0x21 | Operation_status | R | G | B | ... | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation successful
Index is the starting coordinate of the RGB light, starting from 0. The Angle device has only one RGB light, so Index = 0, Num = 1
The operation failed and the returned data packet did not contain RGB values.

5.3 Set RGB light brightness - `Cmd 0x22`

Request data

Input parameters: Index_id (device index ID), Light (RGB brightness, 0~100, default 40), Save_to_flash (whether to save to internal Flash)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x22 | Light | Save_to_flash | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x22 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation successful
Save_to_flash Whether to save internal Flash
- 0: Do not save
- 1：Save
Successful setting takes effect immediately
Saving to the internal Flash requires erasing the page, which is a time-consuming process (about 20ms). During this period, the serial port interrupt will be turned off, and frequent operations will affect the life of the device. If you need to adjust the brightness frequently, please avoid saving to the internal Flash every time.

5.4 Get RGB light brightness - `Cmd 0x23`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x23 | CRC | 55 AA

Response Data

Return parameters: Light (RGB brightness)

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x23 | Light | CRC | 55 AA

Things to note

5.5 Read Angle’s 12bit ADC - `Cmd 0x30`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x30 | CRC | 55 AA

Response Data

Return parameter: ADC value

Response Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x30 | ADC_low | ADC_high | CRC | 55 AA

Things to note

Angle_ADC = (uint16_t)((ADC_high << 8) | ADC_low)
The theoretical value range is 0 ~ 4095, but due to device differences, there is an error offset of 0 ~ 10 in the upper and lower limits, so the actual available range will be reduced accordingly.

5.6 Read Angle’s 8bit ADC - `Cmd 0x31`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x31 | CRC | 55 AA

Response Data

Return parameter: ADC value

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x31 | ADC | CRC | 55 AA

Things to note

Angle_ADC = ADC
The theoretical value range is 0 ~ 255, but due to device differences, there is an error offset of 0 ~ 3 in the upper and lower limits, so the actual available range will be reduced accordingly.

5.7 Set the rotation control status to determine whether the encoder value increases or decreases when rotating clockwise - `Cmd 0x32`

Request data

Input parameters: Index_id (device index ID), Clockwise_direct (clockwise status direction), Save_to_flash (whether to save the configuration to the internal Flash)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x32 | Clockwise_direct | Save_to_flash | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x32 | Operation_status | CRC | 55 AA

Things to note

Clockwise_direct encoder direction
- 0: Decrease clockwise
- 1: increasing clockwise (default state)
Operation_status operation status
- 0: Operation failed
- 1: Operation successful
Save_to_flash Whether to save internal Flash
- 0: Do not save
- 1：Save
Successful setting takes effect immediately
Saving to the internal Flash requires erasing the page, which is a time-consuming process (about 20ms). During this period, the serial port interrupt will be turned off, and frequent operations will affect the life of the device.

5.8 Get rotation control status - `Cmd 0x33`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x33 | CRC | 55 AA

Response Data

Return parameter: Clockwise_direct value

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x33 | Clockwise_direct | CRC | 55 AA

Things to note

Clockwise_direct encoder direction
- 0: Decrease clockwise
- 1: increasing clockwise (default state)

5.9 Query the unique UID of the device - `Cmd 0xF8`

Request data

Input parameters: Index_id (device index ID), UID_Type

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xF8 | UID_Type | CRC | 55 AA

Response Data

Return parameters: Operation_status, UID

Response Frame:
  AA 55 | 0x04+4/12 | 0x00 | Index_id | 0xF8 | Operation_status | UID (multi-byte) | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation successful
UID_Type UID type
- 0：4byte UID
- 1：12byte UID

5.10 Query the upgrade program version number - `Cmd 0xF9`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xF9 | CRC | 55 AA

Response Data

Return parameters: Bootloader_version

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xF9 | Bootloader_version | CRC | 55 AA

Things to note

5.11 Query the device software version number - `Cmd 0xFA`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xFA | CRC | 55 AA

Response Data

Return parameters: Firmware_version

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xFA | Firmware_version | CRC | 55 AA

Things to note

5.12 Query device type - `Cmd 0xFB`

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xFB | CRC | 55 AA

Response Data

Return parameters: Device_type

Response Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xFB | Device_type_low | Device_type_high | CRC | 55 AA

Things to note

Device_type = (uint16_t)((Device_type_high << 8) | Device_type_low)
The device type code of Angle is 0x0002

5.13 Enumeration request, sent by the end device of chain link change, and sent when the device is powered on, notifying the host to update the link device status - `Cmd 0xFC`

Request data

Input parameters: none

Request Frame:
  Device-initiated report，No host request frame

Response Data

Return parameters: none

Response Frame:
  Device-initiated report，No response frame

Things to note

None.

5.14 Heartbeat packet, regular communication between chain devices, you can self-discover whether it is an end device, and the host can also use the heartbeat packet to determine whether there is a chain device connection - `Cmd 0xFD`

Request data

Input parameters: none

Request Frame:
  AA 55 | 0x03 | 0x00 | 0xFF | 0xFD | CRC | 55 AA

Response Data

Return parameters: none

Response Frame:
  AA 55 | 0x03 | 0x00 | 0xFF | 0xFD | CRC | 55 AA

Things to note

5.15 Users can obtain the number of link devices through enumeration - `Cmd 0xFE`

Request data

Input parameter: Send_num (default 0, used to record the number of devices)

Request Frame:
  AA 55 | 0x04 | 0x00 | 0xFF | 0xFE | Send_num | CRC | 55 AA

Response Data

Return parameter: Receive_num (the value represents the number of devices)

Response Frame:
  AA 55 | 0x04 | 0x00 | 0xFF | 0xFE | Receive_num | CRC | 55 AA

Things to note

None.

6. Status code/enumeration value

6.1 Operating status

value	Name	Description
`0`	Failure	Operation failed
`1`	Success	Operation successful

Other modes, ranges, and event enumeration values are defined in the "Notes" of the corresponding instructions.

7. Version records

Document version	Date	Description
`V1`	2025-10-23	Organized according to the official Chain Angle protocol

Chain Angle UART Control Protocol (Documentation V1)

1. Basic Information

2. Data Frame Format

2.1 Request Frame Format

2.2 Response Frame Format

2.3 Response Data Convention

3. Checksum

3.1 Checksum Example

4. Quick overview of commands

5. Command Details

5.1 Set RGB value - Cmd 0x20

Request data

Response Data

Things to note

5.2 Get RGB value - Cmd 0x21

Request data

Response Data

Things to note

5.3 Set RGB light brightness - Cmd 0x22

Request data

Response Data

Things to note

5.4 Get RGB light brightness - Cmd 0x23

Request data

Response Data

Things to note

5.5 Read Angle’s 12bit ADC - Cmd 0x30

Request data

Response Data

Things to note

5.6 Read Angle’s 8bit ADC - Cmd 0x31

Request data

Response Data

Things to note

5.7 Set the rotation control status to determine whether the encoder value increases or decreases when rotating clockwise - Cmd 0x32

Request data

Response Data

Things to note

5.8 Get rotation control status - Cmd 0x33

Request data

Response Data

Things to note

5.9 Query the unique UID of the device - Cmd 0xF8

Request data

Response Data

Things to note

5.10 Query the upgrade program version number - Cmd 0xF9

Request data

Response Data

Things to note

5.11 Query the device software version number - Cmd 0xFA

Request data

Response Data

Things to note

5.12 Query device type - Cmd 0xFB

Request data

Response Data

Things to note

5.13 Enumeration request, sent by the end device of chain link change, and sent when the device is powered on, notifying the host to update the link device status - Cmd 0xFC

Request data

Response Data

Things to note

5.14 Heartbeat packet, regular communication between chain devices, you can self-discover whether it is an end device, and the host can also use the heartbeat packet to determine whether there is a chain device connection - Cmd 0xFD

Request data

Response Data

Things to note

5.15 Users can obtain the number of link devices through enumeration - Cmd 0xFE

Request data

Response Data

Things to note

6. Status code/enumeration value

6.1 Operating status

7. Version records

5.1 Set RGB value - `Cmd 0x20`

5.2 Get RGB value - `Cmd 0x21`

5.3 Set RGB light brightness - `Cmd 0x22`

5.4 Get RGB light brightness - `Cmd 0x23`

5.5 Read Angle’s 12bit ADC - `Cmd 0x30`

5.6 Read Angle’s 8bit ADC - `Cmd 0x31`

5.7 Set the rotation control status to determine whether the encoder value increases or decreases when rotating clockwise - `Cmd 0x32`

5.8 Get rotation control status - `Cmd 0x33`

5.9 Query the unique UID of the device - `Cmd 0xF8`

5.10 Query the upgrade program version number - `Cmd 0xF9`

5.11 Query the device software version number - `Cmd 0xFA`

5.12 Query device type - `Cmd 0xFB`

5.13 Enumeration request, sent by the end device of chain link change, and sent when the device is powered on, notifying the host to update the link device status - `Cmd 0xFC`

5.14 Heartbeat packet, regular communication between chain devices, you can self-discover whether it is an end device, and the host can also use the heartbeat packet to determine whether there is a chain device connection - `Cmd 0xFD`

5.15 Users can obtain the number of link devices through enumeration - `Cmd 0xFE`