Chain Mono UART Control Protocol (Documentation V1.0)

1. Basic Information

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

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

2.2 Response Frame Format

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

2.3 Response Data Convention

3. Checksum

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

5. Command Details

5.1 Set display mode - Cmd 0x10

Request data

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

Request Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x10 | 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

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
2. Mode display mode (default 0)
   • 0: Pixel control mode (directly set pixel display)
   • 1: Scroll character mode (scrolling display string)

5.2 Get display mode - Cmd 0x11

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x11 | CRC | 55 AA

Response Data

Return parameters: Mode (display mode)

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

Things to note

1. Mode display mode (default 0)
   • 0: Pixel control mode (directly set pixel display)
   • 1: Scroll character mode (scrolling display string)

5.3 Set pixels - Cmd 0x30

Request data

Input parameters: Index_id (device index ID), Num (number of pixels to be set), Draw_pixel (pixel value setting, including XY coordinates)

Request Frame:
  AA 55 | 0x04 + Num | 0x00 | Index_id | 0x30 | Num | Draw_pixel0 | Draw_pixel1 | Draw_pixel2 | Draw_pixel3 | ... | 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

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
   • 2: Mode mismatch (needs to be configured as pixel control mode)
2. Num range: 1 ~ 64
3. Draw_pixel bit [7]: reserved bit [6]: Status (0=off, 1=on) bit [5:3]: X coordinate (0-7) bit [2:0]: Y coordinate (0-7)

5.4 Full-screen display cache refresh - Cmd 0x31

Request data

Input parameters: Index_id (device index ID), Display_buffer (full-screen display cache)

Request Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x31 | Display_buffer0 | Display_buffer1 | Display_buffer2 | Display_buffer3 | ... | Display_buffer7 | 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

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
   • 2: Mode mismatch (needs to be configured as pixel control mode)
2. Display_buffer Display_buffer0 → Y: The 0th row of data Display_buffer1 → Y: The 1st row of data ... Bit7→Bit0 corresponds to X coordinate 0→7, high bit first 0=off, 1=on

5.5 Get pixel value - Cmd 0x32

Request data

Input parameters: Index_id (device index ID), Num (number of pixels to be obtained), Coordinate_xy (pixel coordinates)

Request Frame:
  AA 55 | 0x04 + Num | 0x00 | Index_id | 0x32 | Num | Coordinate_xy0 | Coordinate_xy1 | Coordinate_xy2 | Coordinate_xy3 | ... | CRC | 55 AA

Response Data

Return parameters: Pixel_state (pixel value)

Response Frame:
  AA 55 | 0x03 + Num | 0x00 | Index_id | 0x32 | Pixel_state0 | Pixel_state1 | Pixel_state2 | Pixel_state3 | ... | CRC | 55 AA

Things to note

1. Coordinate_xy bit[7:6]: reserved bit[5:3]: X coordinate (0-7) bit[2:0]: Y coordinate (0-7)
2. Pixel_state
   • 0: off
   • 1: bright

5.6 Get full-screen display cache - 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 parameters: Display_buffer (full screen display cache)

Response Frame:
  AA 55 | 0x0B | 0x00 | Index_id | 0x33 | Display_buffer0 | Display_buffer1 | Display_buffer2 | Display_buffer3 | ... | Display_buffer7 | CRC | 55 AA

Things to note

1. Display_buffer Display_buffer0 → Y: The 0th row of data Display_buffer1 → Y: The 1st row of data ... Bit7→Bit0 corresponds to X coordinate 0→7, high bit first 0=off, 1=on,

5.7 Display characters - Cmd 0x34

Request data

Input parameters: Index_id (device index ID), Char (ASCII code of the character to be displayed), Offset (displayed position offset)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0x34 | Char | Offset | CRC | 55 AA

Response Data

Return parameters: Operation_status

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

Things to note

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
   • 2: Mode mismatch (needs to be configured as pixel control mode)
2. Char To display the ASCII code of characters, English letters, numbers and symbols with ASCII codes between 32~127 are supported, and the font size is 5x7
3. Offset [7:4]: x-axis offset, 0 ~ 7 [3:0]: y-axis offset, 0 ~ 7

5.8 Display scrolling string - Cmd 0x40

Request data

Input parameters: Index_id (device index ID), Scroll_mode (scrolling mode), Scroll_interval (scrolling speed), String_length (string length), char (character)

Request Frame:
  AA 55 | 0x07+String_length | 0x00 | Index_id | 0x40 | Scroll_mode | Scroll_interval_low | Scroll_interval_high | String_length | char1 | ... | 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

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
   • 2: Pattern mismatch (rolling character mode needs to be configured)
2. Scroll_mode [7:4]: Scroll direction 0: Scroll right, 1: Scroll left, 2: Scroll up, 3: Scroll down [3:0]: Scroll mode 0: Play once and stop, 1: Scroll in a loop, 2: Bounce back and forth
3. Scroll_interval Scroll_interval movement speed unit is ms/pixel, each Scroll_interval time moves one pixel Scroll_interval =( uint16_t )(( Scroll_interval_high << 8 ) | Scroll_interval_low ) Range 0~65535, unit ms/pixel
4. String_length Length of rolling string
5. char The displayed characters support English letters, numbers and symbols with ASCII codes between 32~127, and the font size is 5x7

5.9 Get scrolling string - Cmd 0x41

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0x41 | CRC | 55 AA

Response Data

Return parameters: Scroll_mode (scrolling mode), Scroll_interval_low, Scroll_interval_high (scrolling speed), String_length (string length), char (character)

Response Frame:
  AA 55 | 0x07+String_length | 0x00 | Index_id | 0x41 | Scroll_mode | Scroll_interval_low | Scroll_interval_high | String_length | Char1 | ... | CRC | 55 AA

Things to note

1. Scroll_mode [7:4]: Scroll direction 0: Scroll right, 1: Scroll left, 2: Scroll up, 3: Scroll down [3:0]: Scroll mode 0: Play once and stop, 1: Scroll in a loop, 2: Bounce back and forth
2. Scroll_interval Scroll_interval movement speed unit is ms/pixel, each Scroll_interval time moves one pixel Scroll_interval =( uint16_t )(( Scroll_interval_high << 8 ) | Scroll_interval_low ) Range 0~65535, unit ms/pixel
3. String_length Length of rolling string
4. Char The displayed characters support English letters, numbers and symbols with ASCII codes between 32~127, and the font size is 5x7

5.10 Set scrolling string status - Cmd 0x42

Request data

Input parameters: Index_id (device index ID), Scroll_state (scrolling state)

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

Response Data

Return parameters: Operation_status

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

Things to note

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
   • 2: Pattern mismatch (rolling character mode needs to be configured)
2. Scroll_state
   • 0: Start/continue scrolling
   • 1: Pause scrolling (the screen keeps the current character displayed statically)
   • 2: Stop and clear (clear the displayed characters and start from the beginning next time the setting is started)

5.11 Set scrolling string status - Cmd 0x43

Request data

Input parameter: Index_id (device index ID)

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

Response Data

Return parameters: Scroll_state (scrolling state)

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0x43 | Scroll_state | CRC | 55 AA

Things to note

1. Scroll_state
   • 0: scrolling
   • 1: suspended state
   • 2: idle/stop state

5.12 Set screen rotation angle - Cmd 0xE0

Request data

Input parameters: Index_id (device index ID), Screen_Rotation (screen rotation angle), Save_to_flash (whether to save to internal Flash)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xE0 | Screen_Rotation | Save_to_flash | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xE0 | Operation_status | CRC | 55 AA

Things to note

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
2. Screen_Rotation
   • 0: Default display angle
   • 1: Rotate 90° clockwise
   • 2: Rotate 180° clockwise
   • 3: Rotate 270° clockwise (90° counterclockwise)
3. Save_to_flash Whether to save internal Flash
   • 0: Do not save
   • 1：Save
4. Successful setting takes effect immediately
5. 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.

5.13 Get the screen rotation angle - Cmd 0xE1

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xE1 | CRC | 55 AA

Response Data

Return parameters: Screen_Rotation (screen rotation angle)

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xE1 | Screen_Rotation | CRC | 55 AA

Things to note

1. Screen_Rotation
   • 0: Default display angle
   • 1: Rotate 90° clockwise
   • 2: Rotate 180° clockwise
   • 3: Rotate 270° clockwise (90° counterclockwise)

5.14 Set screen brightness level - Cmd 0xE2

Request data

Input parameters: Index_id (device index ID), Brightness_level (screen brightness level), Save_to_flash (whether to save to internal Flash)

Request Frame:
  AA 55 | 0x05 | 0x00 | Index_id | 0xE2 | Brightness_level | Save_to_flash | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xE2 | Operation_status | CRC | 55 AA

Things to note

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
2. Brightness_level 0-7: 7 brightness levels, default 7
3. Save_to_flash Whether to save internal Flash
   • 0: Do not save
   • 1：Save
4. Successful setting takes effect immediately
5. 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.

5.15 Get the screen rotation angle - Cmd 0xE3

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xE3 | CRC | 55 AA

Response Data

Return parameters: Brightness_level (screen brightness level)

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xE3 | Brightness_level | CRC | 55 AA

Things to note

1. Brightness_level 0-7: 7 brightness levels, default 7

5.16 Clear screen - Cmd 0xE4

Request data

Input parameter: Index_id (device index ID)

Request Frame:
  AA 55 | 0x03 | 0x00 | Index_id | 0xE4 | CRC | 55 AA

Response Data

Return parameters: Operation_status

Response Frame:
  AA 55 | 0x04 | 0x00 | Index_id | 0xE4 | Operation_status | CRC | 55 AA

Things to note

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful

5.17 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

1. Operation_status operation status
   • 0: Operation failed
   • 1: Operation successful
2. UID_Type UID type
   • 0：4byte UID
   • 1：12byte UID

5.18 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

None.

5.19 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

None.

5.20 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

1. Device_type = (uint16_t)((Device_type_high << 8) | Device_type_low)
2. The device type code of Mono is 0x000D None

5.21 Enumeration request, sent by the end device of chain link change, and sent by the device when it 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.

5.22 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

None.

5.23 Enumerate to obtain the number of cascaded devices - 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

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

7. Version records