Unit 8Servos2-Chain UART Control Protocol (Documentation V1)

1. Basic Information

Item	Description
Communication method	UART / serial port asynchronous communication
Device	Unit 8Servos2-Chain
SKU	U223
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 sent low byte first.

The maximum packet length is 256 bytes. The Length field is the number of bytes from Index to CRC, including Index and CRC but excluding the header, the tail and the Length field itself.

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	Index ID of the device in the Chain link
Cmd	1	Request command code
Req Data	n	Request parameters; the length is `0` when there are no parameters
CRC	1	See "3. Checksum"
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	Index ID of the device in the Chain link
Cmd	1	Same as the request `Cmd`
Resp Data	n	Response data, whose structure is defined by the corresponding command
CRC	1	See "3. Checksum"
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
Response with a status code	`Operation_status = 0` means the operation failed; `Operation_status = 1` means the operation succeeded
Response without a status code	How success or failure is determined follows the "Notes" of the corresponding command

3. Checksum

Item	rules
Check field	`CRC`
Checksum range	From `Index` up to the last byte of `Data`
Checksum algorithm	Excluding the header, the tail, `Length` and `CRC`; the remaining bytes are summed and the low 8 bits are used
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
`0x10`	Set mode (single)	`0x0005`	`0x0004`	Index_id (device index ID), GPIO (channel), Mode (mode)	Operation_status	`5.1`
`0x11`	Set mode (multiple)	`0x000B`	`0x0004`	Index_id (device index ID), Mode (mode)	Operation_status	`5.2`
`0x12`	Get mode (single)	`0x0004`	`0x0004/0x0005`	Index_id (device index ID), GPIO (channel)	Operation_status, Mode (mode)	`5.3`
`0x13`	Get mode (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	Mode (mode)	`5.4`
`0x30`	Set input pull-up/pull-down (single)	`0x0005`	`0x0004`	Index_id (device index ID), GPIO (channel), PU/PD (input pull-up/pull-down configuration)	Operation_status	`5.5`
`0x31`	Set input pull-up/pull-down (multiple)	`0x000B`	`0x0004`	Index_id (device index ID), PU/PD (input pull-up/pull-down configuration)	Operation_status	`5.6`
`0x32`	Get input pull-up/pull-down (single)	`0x0004`	`0x0004/0x0005`	Index_id (device index ID), GPIO (channel)	Operation_status, PU/PD (input pull-up/pull-down configuration)	`5.7`
`0x33`	Get input pull-up/pull-down (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	PU/PD (input pull-up/pull-down configuration)	`5.8`
`0x34`	Get input level (single)	`0x0004`	`0x0005/0x0004`	Index_id (device index ID), GPIO (channel)	Operation_status, Level (input level)	`5.9`
`0x35`	Get input level (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	Level (input level)	`5.10`
`0x40`	Set output level (single)	`0x0005`	`0x0004`	Index_id (device index ID), GPIO (channel), Level (output level)	Operation_status	`5.11`
`0x41`	Set output level (multiple)	`0x000B`	`0x0004`	Index_id (device index ID), Level (output level)	Operation_status	`5.12`
`0x42`	Get output level (single)	`0x0004`	`0x0004/0x0005`	Index_id (device index ID), GPIO (channel)	Operation_status, Level (output level)	`5.13`
`0x43`	Get output level (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	Level (output level)	`5.14`
`0x50`	Get ADC channel value (single)	`0x0004`	`0x0004/0x0006`	Index_id (device index ID), GPIO (channel)	Operation_status, ADC	`5.15`
`0x51`	Get ADC channel value (multiple)	`0x0003`	`0x0013`	Index_id (device index ID)	ADC	`5.16`
`0x60`	Set Angle (single)	`0x0005`	`0x0004`	Index_id (device index ID), GPIO (channel), Angle (servo angle)	Operation_status	`5.17`
`0x61`	Set Angle (multiple)	`0x000B`	`0x0004`	Index_id (device index ID), Angle (servo angle)	Operation_status	`5.18`
`0x62`	Get Angle (single)	`0x0004`	`0x0004/0x0005`	Index_id (device index ID), GPIO (channel)	Operation_status, Angle (servo angle)	`5.19`
`0x63`	Get Angle (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	Angle (servo angle)	`5.20`
`0x70`	Set RGB configuration (single)	`0x0005`	`0x0004`	Index_id (device index ID), GPIO (channel), RGB (RGB configuration)	Operation_status	`5.21`
`0x71`	Set RGB configuration (multiple)	`0x000B`	`0x0004`	Index_id (device index ID), RGB (RGB configuration)	Operation_status	`5.22`
`0x72`	Get RGB configuration (single)	`0x0004`	`0x0004/0x0005`	Index_id (device index ID), GPIO (channel)	Operation_status, RGB (RGB configuration)	`5.23`
`0x73`	Get RGB configuration (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	RGB0 ~ RGB7 (RGB configuration of each channel)	`5.24`
`0x74`	Set RGB buffer (single)	`0x0007`	`0x0004`	Index_id (device index ID), Index (channel), R, G, B (color)	Operation_status	`5.25`
`0x75`	Set RGB buffer (multiple)	`0x0033`	`0x0003`	Index_id (device index ID), R, G, B (color)	None	`5.26`
`0x76`	Get RGB buffer (single)	`0x0004`	`0x0004/0x0007`	Index_id (device index ID), Index (channel)	Operation_status, R, G, B (color)	`5.27`
`0x77`	Get RGB buffer (multiple)	`0x0003`	`0x0033`	Index_id (device index ID)	R0 ~ B15 (16 sets of RGB buffer values)	`5.28`
`0x80`	Set PWM duty cycle (single)	`0x0005`	`0x0004`	Index_id (device index ID), GPIO (channel), Duty (duty cycle)	Operation_status	`5.29`
`0x81`	Set PWM duty cycle (multiple)	`0x000B`	`0x0004`	Index_id (device index ID), Duty (duty cycle)	Operation_status	`5.30`
`0x82`	Get PWM duty cycle (single)	`0x0004`	`0x0004/0x0005`	Index_id (device index ID), GPIO (channel)	Operation_status, Duty (duty cycle)	`5.31`
`0x83`	Get PWM duty cycle (multiple)	`0x0003`	`0x000B`	Index_id (device index ID)	Duty0 ~ Duty7 (duty cycle of each channel)	`5.32`
`0x90`	Set timer frequency (single)	`0x0006`	`0x0004`	Index_id (device index ID), Time (channel), Freq (frequency)	Operation_status	`5.33`
`0x91`	Set timer frequency (multiple)	`0x0007`	`0x0004`	Index_id (device index ID), Freq (frequency)	Operation_status	`5.34`
`0x92`	Get timer frequency (single)	`0x0004`	`0x0004/0x0006`	Index_id (device index ID), Time (channel)	Operation_status, Freq (frequency)	`5.35`
`0x93`	Get timer frequency (multiple)	`0x0003`	`0x0007`	Index_id (device index ID)	Freq0_L ~ Freq1_H (TIM2 / TIM3 frequency)	`5.36`
`0xA0`	Get reference voltage	`0x0003`	`0x0005`	Index_id (device index ID)	Operation_status, Voltage (unit mV)	`5.37`
`0xA1`	Get GROVE voltage	`0x0003`	`0x0005`	Index_id (device index ID)	Operation_status, Voltage (unit mV)	`5.38`
`0xA2`	Get DC port voltage	`0x0003`	`0x0005`	Index_id (device index ID)	Operation_status, Voltage (unit mV)	`5.39`
`0xA3`	Get system current	`0x0003`	`0x0005`	Index_id (device index ID)	Operation_status, Current (unit mA)	`5.40`
`0xF8`	Query device unique UID	`0x0004`	`0x0004+4/12`	Index_id (device index ID), UID_Type	Operation_status, UID	`5.41`
`0xF9`	Query the upgrade program version number	`0x0003`	`0x0004`	Index_id (device index ID)	Bootloader_version	`5.42`
`0xFA`	Query the device software version number	`0x0003`	`0x0004`	Index_id (device index ID)	Firmware_version	`5.43`
`0xFB`	Query device type	`0x0003`	`0x0005`	Index_id (device index ID)	Device_type	`5.44`
`0xFC`	Enumeration request, sent by the end device when the Chain link changes and when the device is powered on, notifying the host to update the link device status	`Device-initiated report`	`Device-initiated report`	none	none	`5.45`
`0xFD`	Heartbeat packet, periodic communication between Chain devices, which can self-discover whether a device is the end device; the host can also use heartbeat packets to determine whether a Chain device is connected	`0x0003`	`0x0003`	none	none	`5.46`
`0xFE`	Enumerate the number of cascaded devices	`0x0004`	`0x0004`	Send_num (default 0, used to record the number of devices)	Receive_num (the value represents the number of devices)	`5.47`

5. Command Details

5.1 Set mode (single) - `Cmd 0x10`

Request data

Input parameters: Index_id (device index ID), GPIO (channel), Mode (mode)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x10 | GPIO | Mode | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x10 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Mode
- 0: Input
- 1: Output
- 2: ADC
- 3: Servo
- 4: RGB (WS2812)
- 5: PWM
- default: 0

5.2 Set mode (multiple) - `Cmd 0x11`

Request data

Input parameters: Index_id (device index ID), Mode (mode)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x11 | Mode0 | Mode1 | Mode2 | Mode3 | ... | Mode7 | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x11 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Mode
- 0: Input
- 1: Output
- 2: ADC
- 3: Servo
- 4: RGB
- 5: PWM
- default: 0

5.3 Get mode (single) - `Cmd 0x12`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x12 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, Mode (mode)

Response Frame:
  AA 55 | 0x04/0x05 | 0x00 | Index_id | 0x12 | Operation_status | Mode | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Mode
- 0: Input
- 1: Output
- 2: ADC
- 3: Servo
- 4: RGB
- 5: PWM
- default: 0
The response length is 0x05 on success and 0x04 on failure

5.4 Get mode (multiple) - `Cmd 0x13`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x13 | CRC | 55 AA

Response Data

Return parameters: Mode (mode)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x13 | Mode0 | Mode1 | Mode2 | Mode3 | ... | Mode7 | CRC | 55 AA

Things to note

Mode
- 0: Input
- 1: Output
- 2: ADC
- 3: Servo
- 4: RGB
- 5: PWM
- default: 0

5.5 Set input pull-up/pull-down (single) - `Cmd 0x30`

Request data

Input parameters: Index_id (device index ID), GPIO (channel), PU/PD (input pull-up/pull-down configuration)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x30 | GPIO | PU/PD | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x30 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
PU/PD pull-up/pull-down configuration
- 0: No pull-up/pull-down
- 1: Pull-up
- 2: Pull-down
- default: 0

5.6 Set input pull-up/pull-down (multiple) - `Cmd 0x31`

Request data

Input parameters: Index_id (device index ID), PU/PD (input pull-up/pull-down configuration)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x31 | PU/PD0 | PU/PD1 | PU/PD2 | PU/PD3 | ... | PU/PD7 | CRC | 55 AA

Response Data

Return parameters: Operation_status

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

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
PU/PD pull-up/pull-down configuration
- 0: No pull-up/pull-down
- 1: Pull-up
- 2: Pull-down
- default: 0

5.7 Get input pull-up/pull-down (single) - `Cmd 0x32`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x32 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, PU/PD (input pull-up/pull-down configuration)

Response Frame:
  AA 55 | 0x04/0x05 | 0x00 | Index_id | 0x32 | Operation_status | PU/PD | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
PU/PD pull-up/pull-down configuration
- 0: No pull-up/pull-down
- 1: Pull-up
- 2: Pull-down
- default: 0
The response length is 0x05 on success and 0x04 on failure

5.8 Get input pull-up/pull-down (multiple) - `Cmd 0x33`

Request data

Input parameters: Index_id (device index ID)

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

Response Data

Return parameters: PU/PD (input pull-up/pull-down configuration)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x33 | PU/PD0 | PU/PD1 | PU/PD2 | PU/PD3 | ... | PU/PD7 | CRC | 55 AA

Things to note

PU/PD pull-up/pull-down configuration
- 0: No pull-up/pull-down
- 1: Pull-up
- 2: Pull-down
- default: 0

5.9 Get input level (single) - `Cmd 0x34`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x34 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, Level (input level)

Response Frame:
  AA 55 | 0x05/0x04 | 0x00 | Index_id | 0x34 | Operation_status | Level | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Level input level
- 1: High level
- 0: Low level
The response length is 0x05 on success and 0x04 on failure

5.10 Get input level (multiple) - `Cmd 0x35`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x35 | CRC | 55 AA

Response Data

Return parameters: Level (input level)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x35 | Level0 | Level1 | Level2 | Level3 | ... | Level7 | CRC | 55 AA

Things to note

Level input level
- 1: High level
- 0: Low level

5.11 Set output level (single) - `Cmd 0x40`

Request data

Input parameters: Index_id (device index ID), GPIO (channel), Level (output level)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x40 | GPIO | Level | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x40 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Level output level
- 1: High level
- 0: Low level

5.12 Set output level (multiple) - `Cmd 0x41`

Request data

Input parameters: Index_id (device index ID), Level (output level)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x41 | Level0 | Level1 | Level2 | Level3 | ... | Level7 | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x41 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Level output level
- 1: High level
- 0: Low level

5.13 Get output level (single) - `Cmd 0x42`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x42 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, Level (output level)

Response Frame:
  AA 55 | 0x04/0x05 | 0x00 | Index_id | 0x42 | Operation_status | Level | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Level output level
- 1: High level
- 0: Low level
The response length is 0x05 on success and 0x04 on failure

5.14 Get output level (multiple) - `Cmd 0x43`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x43 | CRC | 55 AA

Response Data

Return parameters: Level (output level)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x43 | Level0 | Level1 | Level2 | Level3 | ... | Level7 | CRC | 55 AA

Things to note

Level output level
- 1: High level
- 0: Low level

5.15 Get ADC channel value (single) - `Cmd 0x50`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x50 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, ADC

Response Frame:
  AA 55 | 0x04/0x06 | 0x00 | Index_id | 0x50 | Operation_status | ADC_L | ADC_H | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
ADC: 0~4095
If the GPIO channel being read is not configured for ADC mode, the returned value is always 0
The response length is 0x06 on success and 0x04 on failure

5.16 Get ADC channel value (multiple) - `Cmd 0x51`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x51 | CRC | 55 AA

Response Data

Return parameters: ADC

Response Frame:
  AA 55 | 0x13 | 0x00 | Index_id | 0x51 | ADC0_L | ADC0_H | ADC1_L | ADC1_H | ... | ADC7_H | CRC | 55 AA

Things to note

ADC: 0~4095
If the GPIO channel being read is not configured for ADC mode, the returned value is always 0

5.17 Set Angle (single) - `Cmd 0x60`

Request data

Input parameters: Index_id (device index ID), GPIO (channel), Angle (servo angle)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x60 | GPIO | Angle | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x60 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Angle
- 0~180
- default: 0

5.18 Set Angle (multiple) - `Cmd 0x61`

Request data

Input parameters: Index_id (device index ID), Angle (servo angle)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x61 | Angle0 | Angle1 | Angle2 | Angle3 | ... | Angle7 | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x61 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Angle
- 0~180
- default: 0

5.19 Get Angle (single) - `Cmd 0x62`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x62 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, Angle (servo angle)

Response Frame:
  AA 55 | 0x04/0x05 | 0x00 | Index_id | 0x62 | Operation_status | Angle | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Angle
- 0~180
- default: 0
The response length is 0x05 on success and 0x04 on failure

5.20 Get Angle (multiple) - `Cmd 0x63`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x63 | CRC | 55 AA

Response Data

Return parameters: Angle (servo angle)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x63 | Angle0 | Angle1 | Angle2 | Angle3 | ... | Angle7 | CRC | 55 AA

Things to note

Angle
- 0~180
- default: 0

5.21 Set RGB configuration (single) - `Cmd 0x70`

Request data

Input parameters: Index_id (device index ID), GPIO (channel), RGB (RGB configuration)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x70 | GPIO | RGB | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x70 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
RGB configuration
- bit[7:6]: Reserved
- bit[5]: Refresh bit
- bit[4~0]: Number of RGB LEDs (1~16)
- default: 0
Refresh condition: first set the corresponding GPIO channel to RGB mode, then configure the buffer, the LED count and the refresh bit; the refresh bit is cleared automatically after the refresh (it is also cleared automatically when the channel is not in RGB mode)

5.22 Set RGB configuration (multiple) - `Cmd 0x71`

Request data

Input parameters: Index_id (device index ID), RGB (RGB configuration)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x71 | RGB0 | RGB1 | RGB2 | RGB3 | ... | RGB7 | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x71 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
RGB configuration
- bit[7:6]: Reserved
- bit[5]: Refresh bit
- bit[4~0]: Number of RGB LEDs (1~16)
- default: 0
Refresh condition: first set the corresponding GPIO channel to RGB mode, then configure the buffer, the LED count and the refresh bit; the refresh bit is cleared automatically after the refresh (it is also cleared automatically when the channel is not in RGB mode)

5.23 Get RGB configuration (single) - `Cmd 0x72`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x72 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, RGB (RGB configuration)

Response Frame:
  AA 55 | 0x04/0x05 | 0x00 | Index_id | 0x72 | Operation_status | RGB | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
RGB configuration
- bit[7:6]: Reserved
- bit[5]: Refresh bit
- bit[4~0]: Number of RGB LEDs (1~16)
- default: 0
Refresh condition: first set the corresponding GPIO channel to RGB mode, then configure the buffer, the LED count and the refresh bit; the refresh bit is cleared automatically after the refresh (it is also cleared automatically when the channel is not in RGB mode)
The response length is 0x05 on success and 0x04 on failure

5.24 Get RGB configuration (multiple) - `Cmd 0x73`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x73 | CRC | 55 AA

Response Data

Return parameters: RGB0 ~ RGB7 (RGB configuration of each channel)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x73 | RGB0 | RGB1 | RGB2 | RGB3 | ... | RGB7 | CRC | 55 AA

Things to note

RGB configuration
- bit[7:6]: Reserved
- bit[5]: Refresh bit
- bit[4~0]: Number of RGB LEDs (1~16)
- default: 0
Refresh condition: first set the corresponding GPIO channel to RGB mode, then configure the buffer, the LED count and the refresh bit; the refresh bit is cleared automatically after the refresh (it is also cleared automatically when the channel is not in RGB mode)

5.25 Set RGB buffer (single) - `Cmd 0x74`

Request data

Input parameters: Index_id (device index ID), Index (channel), R, G, B (color)

Request Frame:
  AA 55 | 0x07 | 0x00 | Index_id | 0x74 | Index | R | G | B | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x74 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Index buffer index: 0~15

5.26 Set RGB buffer (multiple) - `Cmd 0x75`

Request data

Input parameters: Index_id (device index ID), R, G, B (color)

Request Frame:
  AA 55 | 0x33 | 0x00 | Index_id | 0x75 | R0 | G0 | B0 | ... | G15 | B15 | CRC | 55 AA

Response Data

Return parameters: None

Response Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x75 | CRC | 55 AA

Things to note

None.

5.27 Get RGB buffer (single) - `Cmd 0x76`

Request data

Input parameters: Index_id (device index ID), Index (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x76 | Index | CRC | 55 AA

Response Data

Return parameters: Operation_status, R, G, B (color)

Response Frame:
  AA 55 | 0x04/0x07 | 0x00 | Index_id | 0x76 | Operation_status | R | G | B | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Index buffer index: 0~15
The response length is 0x07 on success and 0x04 on failure

5.28 Get RGB buffer (multiple) - `Cmd 0x77`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x77 | CRC | 55 AA

Response Data

Return parameters: R0 ~ B15 (16 sets of RGB buffer values)

Response Frame:
  AA 55 | 0x33 | 0x00 | Index_id | 0x77 | R0 | G0 | B0 | ... | G15 | B15 | CRC | 55 AA

Things to note

None.

5.29 Set PWM duty cycle (single) - `Cmd 0x80`

Request data

Input parameters: Index_id (device index ID), GPIO (channel), Duty (duty cycle)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x80 | GPIO | Duty | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x80 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Duty duty cycle
- 0~100
- default: 0

5.30 Set PWM duty cycle (multiple) - `Cmd 0x81`

Request data

Input parameters: Index_id (device index ID), Duty (duty cycle)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x81 | Duty0 | Duty1 | Duty2 | Duty3 | ... | Duty7 | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x81 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Duty duty cycle
- 0~100
- default: 0

5.31 Get PWM duty cycle (single) - `Cmd 0x82`

Request data

Input parameters: Index_id (device index ID), GPIO (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x82 | GPIO | CRC | 55 AA

Response Data

Return parameters: Operation_status, Duty (duty cycle)

Response Frame:
  AA 55 | 0x04/0x05 | 0x00 | Index_id | 0x82 | Operation_status | Duty | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
GPIO channel: 0~7
Duty duty cycle
- 0~100
- default: 0
The response length is 0x05 on success and 0x04 on failure

5.32 Get PWM duty cycle (multiple) - `Cmd 0x83`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x83 | CRC | 55 AA

Response Data

Return parameters: Duty0 ~ Duty7 (duty cycle of each channel)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x83 | Duty0 | Duty1 | Duty2 | Duty3 | ... | Duty7 | CRC | 55 AA

Things to note

Duty duty cycle
- 0~100
- default: 0

5.33 Set timer frequency (single) - `Cmd 0x90`

Request data

Input parameters: Index_id (device index ID), Time (channel), Freq (frequency)

Request Frame:
  AA 55 | 0x06 | 0x00 | Index_id | 0x90 | Time | Freq_L | Freq_H | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x90 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Time channel
- 0~1
- 0: TIM2
- 1: TIM3
Freq
- 1~65535
- default: 50Hz
TIM2 sets the frequency of the GPIO0~GPIO3 channels and TIM3 sets the frequency of the GPIO4~GPIO7 channels

5.34 Set timer frequency (multiple) - `Cmd 0x91`

Request data

Input parameters: Index_id (device index ID), Freq (frequency)

Request Frame:
  AA 55 | 0x07 | 0x00 | Index_id | 0x91 | Freq0_L | Freq0_H | Freq1_L | Freq1_H | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x91 | Operation_status | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Freq
- 1~65535
- default: 50Hz
TIM2 sets the frequency of the GPIO0~GPIO3 channels and TIM3 sets the frequency of the GPIO4~GPIO7 channels

5.35 Get timer frequency (single) - `Cmd 0x92`

Request data

Input parameters: Index_id (device index ID), Time (channel)

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x92 | Time | CRC | 55 AA

Response Data

Return parameters: Operation_status, Freq (frequency)

Response Frame:
  AA 55 | 0x04/0x06 | 0x00 | Index_id | 0x92 | Operation_status | Freq_L | Freq_H | CRC | 55 AA

Things to note

Operation_status operation status
- 0: Operation failed
- 1: Operation succeeded
Time channel: 0~1
Freq
- 1~65535
- default: 50Hz
TIM2 sets the frequency of the GPIO0~GPIO3 channels and TIM3 sets the frequency of the GPIO4~GPIO7 channels
The response length is 0x06 on success and 0x04 on failure

5.36 Get timer frequency (multiple) - `Cmd 0x93`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x93 | CRC | 55 AA

Response Data

Return parameters: Freq0_L ~ Freq1_H (TIM2 / TIM3 frequency)

Response Frame:
  AA 55 | 0x07 | 0x00 | Index_id | 0x93 | Freq0_L | Freq0_H | Freq1_L | Freq1_H | CRC | 55 AA

Things to note

Freq
- 1~65535
- default: 50Hz
TIM2 sets the frequency of the GPIO0~GPIO3 channels and TIM3 sets the frequency of the GPIO4~GPIO7 channels

5.37 Get reference voltage - `Cmd 0xA0`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xA0 | CRC | 55 AA

Response Data

Return parameters: Operation_status, Voltage (unit mV)

Response Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xA0 | Voltage_L | Voltage_H | CRC | 55 AA

Things to note

None.

5.38 Get GROVE voltage - `Cmd 0xA1`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xA1 | CRC | 55 AA

Response Data

Return parameters: Operation_status, Voltage (unit mV)

Response Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xA1 | Voltage_L | Voltage_H | CRC | 55 AA

Things to note

None.

5.39 Get DC port voltage - `Cmd 0xA2`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xA2 | CRC | 55 AA

Response Data

Return parameters: Operation_status, Voltage (unit mV)

Response Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xA2 | Voltage_L | Voltage_H | CRC | 55 AA

Things to note

None.

5.40 Get system current - `Cmd 0xA3`

Request data

Input parameters: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xA3 | CRC | 55 AA

Response Data

Return parameters: Operation_status, Current (unit mA)

Response Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xA3 | Current_L | Current_H | CRC | 55 AA

Things to note

None.

5.41 Query device unique UID - `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 succeeded
UID_Type UID type
- 0: 4byte UID
- 1: 12byte UID

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

Request data

Input parameters: 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

None.

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

Request data

Input parameters: 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

None.

5.44 Query device type - `Cmd 0xFB`

Request data

Input parameters: 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 the Unit 8Servos2-Chain is 0x000C

5.45 Enumeration request, sent by the end device when the Chain link changes and 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:
  AA 55 | 0x03 | 0x00 | 0xFF | 0xFC | CRC | 55 AA

Things to note

None.

5.46 Heartbeat packet, periodic communication between Chain devices, which can self-discover whether a device is the end device; the host can also use heartbeat packets to determine whether a Chain device is connected - `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

None.

5.47 Enumerate the number of cascaded devices - `Cmd 0xFE`

Request data

Input parameters: 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 parameters: 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 succeeded

Other modes, ranges and event enumeration values are defined in the "Things to note" of the corresponding command.

7. Version records

Document version	Date	Description
`V1`	2026-7-14	Compiled from the official Unit 8Servos2-Chain protocol

Unit 8Servos2-Chain 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 mode (single) - Cmd 0x10

Request data

Response Data

Things to note

5.2 Set mode (multiple) - Cmd 0x11

Request data

Response Data

Things to note

5.3 Get mode (single) - Cmd 0x12

Request data

Response Data

Things to note

5.4 Get mode (multiple) - Cmd 0x13

Request data

Response Data

Things to note

5.5 Set input pull-up/pull-down (single) - Cmd 0x30

Request data

Response Data

Things to note

5.6 Set input pull-up/pull-down (multiple) - Cmd 0x31

Request data

Response Data

Things to note

5.7 Get input pull-up/pull-down (single) - Cmd 0x32

Request data

Response Data

Things to note

5.8 Get input pull-up/pull-down (multiple) - Cmd 0x33

Request data

Response Data

Things to note

5.9 Get input level (single) - Cmd 0x34

Request data

Response Data

Things to note

5.10 Get input level (multiple) - Cmd 0x35

Request data

Response Data

Things to note

5.11 Set output level (single) - Cmd 0x40

Request data

Response Data

Things to note

5.12 Set output level (multiple) - Cmd 0x41

Request data

Response Data

Things to note

5.13 Get output level (single) - Cmd 0x42

Request data

Response Data

Things to note

5.14 Get output level (multiple) - Cmd 0x43

Request data

Response Data

Things to note

5.15 Get ADC channel value (single) - Cmd 0x50

Request data

Response Data

Things to note

5.16 Get ADC channel value (multiple) - Cmd 0x51

Request data

Response Data

Things to note

5.17 Set Angle (single) - Cmd 0x60

Request data

Response Data

Things to note

5.18 Set Angle (multiple) - Cmd 0x61

Request data

5.1 Set mode (single) - `Cmd 0x10`

5.2 Set mode (multiple) - `Cmd 0x11`

5.3 Get mode (single) - `Cmd 0x12`

5.4 Get mode (multiple) - `Cmd 0x13`

5.5 Set input pull-up/pull-down (single) - `Cmd 0x30`

5.6 Set input pull-up/pull-down (multiple) - `Cmd 0x31`

5.7 Get input pull-up/pull-down (single) - `Cmd 0x32`

5.8 Get input pull-up/pull-down (multiple) - `Cmd 0x33`

5.9 Get input level (single) - `Cmd 0x34`

5.10 Get input level (multiple) - `Cmd 0x35`

5.11 Set output level (single) - `Cmd 0x40`

5.12 Set output level (multiple) - `Cmd 0x41`

5.13 Get output level (single) - `Cmd 0x42`

5.14 Get output level (multiple) - `Cmd 0x43`

5.15 Get ADC channel value (single) - `Cmd 0x50`

5.16 Get ADC channel value (multiple) - `Cmd 0x51`

5.17 Set Angle (single) - `Cmd 0x60`

5.18 Set Angle (multiple) - `Cmd 0x61`

5.19 Get Angle (single) - `Cmd 0x62`

5.20 Get Angle (multiple) - `Cmd 0x63`

5.21 Set RGB configuration (single) - `Cmd 0x70`

5.22 Set RGB configuration (multiple) - `Cmd 0x71`

5.23 Get RGB configuration (single) - `Cmd 0x72`

5.24 Get RGB configuration (multiple) - `Cmd 0x73`

5.25 Set RGB buffer (single) - `Cmd 0x74`

5.26 Set RGB buffer (multiple) - `Cmd 0x75`

5.27 Get RGB buffer (single) - `Cmd 0x76`

5.28 Get RGB buffer (multiple) - `Cmd 0x77`

5.29 Set PWM duty cycle (single) - `Cmd 0x80`

5.30 Set PWM duty cycle (multiple) - `Cmd 0x81`

5.31 Get PWM duty cycle (single) - `Cmd 0x82`

5.32 Get PWM duty cycle (multiple) - `Cmd 0x83`

5.33 Set timer frequency (single) - `Cmd 0x90`

5.34 Set timer frequency (multiple) - `Cmd 0x91`

5.35 Get timer frequency (single) - `Cmd 0x92`