Modbus Register Definitions
Last revision 2026/02/06
Modbus Register Definitions for Gravity: BMP585 High-Precision Barometric Pressure Sensor
Register Definitions
| Register Type | Modbus Address Offset (Hex) | Name | Read/Write Permission | Data Range | Default Value | Description |
|---|---|---|---|---|---|---|
| Input Register | 0x0000 | VID | R | 0x3343-0x3343 | 0x3343 | Vendor ID (VID) |
| Input Register | 0x0001 | PID | R | 0x0000-0xFFFF | 0xC299/0xC298 | Product ID (PID) (bmp581/bmp585) BMP581 PID: 0xC299 BMP585 PID: 0xC298 |
| Input Register | 0x0002 | Hardware Version V1.0.0.0 | R | 0x0000-0xFFFF | 0x1000 | Hardware version number: 0x1000 corresponds to V1.0.0.0 |
| Input Register | 0x0003 | Firmware Version V1.0.0.0 | R | 0x0000-0xFFFF | 0x1000 | Software version number: 0x1000 corresponds to V1.0.0.0 |
| Input Register | 0x0004 | Module Device Address | R | 0x0046-0x0047 | 0x0047 | Unique address of the device on the communication bus. Switch the address (0x47, 0x46) via the DIP switch on the sensor. Non-volatile (persists after power-off) and takes effect upon restart. |
| Input Register | 0x0007 | Chip ID | R | 0x0050-0x0050 | 0x0050 | Unique identifier for the sensor chip model |
| Input Register | 0x0008 | Revision ID | R | 0x0032-0x0032 | 0x0032 | Identifier for the design revision of the sensor chip |
| Input Register | 0x0017 | Chip Status | R | 0x0000-0x000F | 0x0000 | Status register containing the current operating state of the chip. 0b0000 0000 0000 0000 Bits 0-1 function as follows: 1. 0b00 (0x0): I2C mode only 2. 0b01 (0x1): SPI MODE1 and MODE2 3. 0b10 (0x2): SPI MODE0 and MODE3 4. 0b11 (0x3): Both SPI and I2C available (auto-configured, default I2C mode). During power-up, the CSB pin should be connected to VDDIO to pull it high. If the CSB pin is set to low level during power-up, the I2C interface will be disabled. 0b0000 0000 0000 0000 Bit 2 function as follows: i3c_err_0: Set to 1 when an SDR parity error occurs 0b0000 0000 0000 0000 Bit 3 function as follows: i3c_err_3: Set to 1 when an s0/s1 error occurs Example: 0b0000 0000 0000 0001 (0x0001) indicates I2C mode only, no i3c_err_0 or i3c_err_3. |
| Input Register | 0x001D | FIFO Count | R | 0x0000-0x00FF | 0x0000 | Number of current data frames in the FIFO buffer |
| Input Register | 0x0023 | Temperature Data XLSB | R | 0x0000-0x00FF | 0x007F | Extra least significant byte of temperature data (TEMP_DATA_7_0) |
| Input Register | 0x0024 | Temperature Data LSB | R | 0x0000-0x00FF | 0x007F | Least significant byte of temperature data (TEMP_DATA_15_8) |
| Input Register | 0x0025 | Temperature Data MSB | R | 0x0000-0x00FF | 0x007F | Most significant byte of temperature data (TEMP_DATA_23_16) 0b0000 0000 0000 0000 0000 0000 DATA_MSB DATA_LSB DATA_XLSB Temperature (°C) = (TEMP_DATA_MSB, TEMP_DATA_LSB, TEMP_DATA_XLSB) / 2¹⁶ |
| Input Register | 0x0026 | Pressure Data XLSB | R | 0x0000-0x00FF | 0x007F | Extra least significant byte of pressure data (PRESS_DATA_7_0) |
| Input Register | 0x0027 | Pressure Data LSB | R | 0x0000-0x00FF | 0x007F | Least significant byte of pressure data (PRESS_DATA_15_8) |
| Input Register | 0x0028 | Pressure Data MSB | R | 0x0000-0x00FF | 0x007F | Most significant byte of pressure data (PRESS_DATA_23_16) The final pressure data consists of: 0b0000 0000 0000 0000 0000 0000 DATA_MSB DATA_LSB DATA_XLSB Pressure (Pa) = (PRESS_DATA_MSB, PRESS_DATA_LSB, PRESS_DATA_XLSB) / 2⁶ |
| Input Register | 0x002D | Interrupt Status | R | 0x0000-0x00FF | 0x0000 | Register containing various interrupt status flags (bit set to 1 indicates interrupt trigger) 0b0000 0000 0000 0000 Bit 0: Data Ready Interrupt 0b0000 0000 0000 0000 Bit 1: FIFO Full 0b0000 0000 0000 0000 Bit 2: FIFO Threshold Triggered 0b0000 0000 0000 0000 Bit 3: Pressure Data Out of Set Threshold Range 0b0000 0000 0000 0000 Bit 4: Power-On Reset (POR) or Software Reset Completed |
| Input Register | 0x002E | Status | R | 0x0000-0x00FF | 0x0002 | Register containing general device status information (bit set to 1 indicates the corresponding status) 0b0000 0000 0000 0000 status_core_rdy (Bit 1): Digital core ready flag 0b0000 0000 0000 0000 status_nvm_rdy (Bit 2): Non-Volatile Memory (NVM) ready flag 0b0000 0000 0000 0000 status_nvm_err (Bit 3): NVM operation error (e.g., power failure, programming timeout) 0b0000 0000 0000 0000 status_nvm_cmd_err (Bit 4): NVM command execution failure (e.g., invalid parameters) 0b0000 0000 0000 0000 st_crack_pass (Bit 7): Hardware crack detection pass flag |
| Input Register | 0x002F | FIFO Data | R | 0x0000-0x00FF | 0x007F | Register for reading FIFO buffer data PT-frame   P-frame T-frame empty-frame |
| Input Register | 0x003E | Effective Oversampling Rate | R | 0x0000-0x00FF | 0x0000 | Register indicating the current effective oversampling rate setting 0b0000 0000 0000 0000 Bits 0-2: Temperature oversampling rate 0b0000 0000 0000 0000 Bits 3-5: Pressure oversampling rate Refer to the Oversampling Rate Configuration Register for specific values. |
| Holding Register | 0x0001 | Module Baud Rate | RW | 0x0000-0x0008 | 0x0003 | Register for setting the communication baud rate 0x0001: 2400 0x0003: 9600 (default) 0x0004: 14400 0x0005: 19200 0x0006: 38400 0x0007: 57600 0x0008: 115200 Other values: 115200 Non-volatile, takes effect upon restart. |
| Holding Register | 0x0002 | Reserved Bits | RW | 0x0000-0xFFFF | 0x0001 | Reserved |
| Holding Register | 0x0019 | Driver Configuration | RW | 0x0000-0x00FF | 0x0030 | Register for configuring output driver strength and characteristics 0b0000 0000 0000 0000 Bit 0 (I2C mode only): Controls the pull-up resistor of the CSB pin: - 0b0 (0x0): Disable pull-up - 0b1 (0x1): Enable pull-up 0b0000 0000 0000 0000 Bit 1: SPI mode selection: - 0b0 (0x0): 4-wire SPI mode - 0b1 (0x1): 3-wire SPI mode (reduces the number of communication pins) 0b0000 0000 0000 0000 Bits 4-7: Driver strength configuration for serial IO pins (SDX, SDO); the most significant bit (MSB) is only effective in I2C mode. |
| Holding Register | 0x001A | Interrupt Configuration | RW | 0x0000-0x00FF | 0x0035 | Register for configuring interrupt trigger conditions and behavior 0b0000 0000 0000 0000 Bit 0: Interrupt Mode: - 0b0 (0x0): Pulsed mode (automatically deasserts after interrupt trigger) - 0b1 (0x1): Latched mode (requires software to clear the interrupt flag) 0b0000 0000 0000 0000 Bit 1: Interrupt Polarity: - 0b0 (0x0): Active low - 0b1 (0x1): Active high 0b0000 0000 0000 0000 Bit 2: Interrupt Pin Type: - 0b0 (0x0): Push-pull output (high driving capability) - 0b1 (0x1): Open-drain output (requires external pull-up) 0b0000 0000 0000 0000 Bit 3: Interrupt Enable: - 0b0 (0x0): Disable interrupt - 0b1 (0x1): Enable interrupt 0b0000 0000 0000 0000 Bits 4-7: Driver strength configuration for the interrupt pin (INT); the most significant bit (MSB) is only effective in open-drain mode. |
| Holding Register | 0x001B | Interrupt Source | RW | 0x0000-0x00FF | 0x0000 | Register for configuring which events can trigger interrupts (- 0b0 (0x0): Disable interrupt; - 0b1 (0x1): Enable interrupt) 0b0000 0000 0000 0000 Bit 0: Data Ready Interrupt Enable: After enabling, triggers an interrupt when the data register update is completed. 0b0000 0000 0000 0000 Bit 1: FIFO Full Interrupt Enable: After enabling, triggers an interrupt when the FIFO buffer is full. 0b0000 0000 0000 0000 Bit 2: FIFO Threshold/Watermark Interrupt Enable: After enabling, triggers an interrupt when the FIFO data volume reaches the threshold. 0b0000 0000 0000 0000 Bit 3: Pressure Data Out-of-Range Interrupt Enable: After enabling, triggers an interrupt when the pressure data exceeds the set range. |
| Holding Register | 0x001C | FIFO Configuration | RW | 0x0000-0x00FF | 0x0000 | Register for configuring the FIFO buffer operation mode 0b0000 0000 0000 0000 Function of Bits 0-4: Set the FIFO trigger threshold (triggers the corresponding action when the data volume reaches this value). Values and descriptions: 0b00000 (0x0): Disable FIFO threshold function (no trigger condition); 0b11111 (0x1F): Set the threshold to 31 frames (triggers the action when the data volume reaches 31 frames). The maximum configurable number of frames varies by data frame type (PT-frame: up to 15 frames; P-frame/T-frame: up to 31 frames) 0b0000 0000 0000 0000 Function of Bit 5: Select the FIFO operating mode. Values and descriptions: 0b0 (0x0): Stream-to-FIFO Mode — Continuously writes data to the FIFO (continues writing even if the FIFO is nearly full); 0b1 (0x1): STOP-on-FULL Mode — Stops writing new data after the FIFO is full (prevents overflow). |
| Holding Register | 0x001E | FIFO Data Frame Type Configuration | RW | 0x0000-0x00FF | 0x0000 | Configure the types of data frames stored in the FIFO 0b0000 0000 0000 0000 Bits 0-1: Select the FIFO frame data source: 0b00 (0x0): FIFO disabled (no data written to FIFO) 0b01 (0x1): Store only temperature data to FIFO 0b10 (0x2): Store only pressure data to FIFO 0b11 (0x3): Store both pressure + temperature data to FIFO 0b0000 0000 0000 0000 Bits 2-4: Set the FIFO downsampling rate (writes to the FIFO every n samples) n = 2ˣ X ranges from 0 (0b000) to 7 (0b111) |
| Holding Register | 0x0031 | Non-Volatile Memory Address | RW | 0x0000-0x00FF | 0x0000 | Register for setting the access address of non-volatile memory |
| Holding Register | 0x0032 | Non-Volatile Memory Data LSB | RW | 0x0000-0x00FF | 0x0000 | Least significant byte of non-volatile memory data |
| Holding Register | 0x0033 | Non-Volatile Memory Data MSB | RW | 0x0000-0x00FF | 0x0000 | Most significant byte of non-volatile memory data |
Common Modbus-RTU Function Codes
| Function Code (Hex) | Name | Function Description |
|---|---|---|
| 0x03 | Read Multiple Registers | Read integers, characters, status words, and floating-point numbers (read N words) — Operates on Holding Registers with byte-level access. |
| 0x04 | Read Input Registers | Read integers, status words, and floating-point numbers (read N words) — Operates on Input Registers with byte-level access. |
| 0x06 | Write Single Holding Register | Write integers, characters, status words, and floating-point numbers (write one word) — Operates on Holding Registers with byte-level access. |
| 0x10 | Write Multiple Holding Registers | Write to multiple consecutive Holding Registers — Load specific binary values into a series of contiguous Holding Registers. |
The above commands enable reading and writing of Input Registers and Holding Registers.
Register Read/Write Examples
Hardware Preparation
- SEN0664 Gravity: BMP585 Barometric Pressure Sensor × 1
- TEL0185 RainbowLink USB Protocol Converter × 1
Recommended Serial Debug Tools & Downloads
For serial communication debugging, professional tools are required. The following commonly used and feature-rich tools are recommended:
- XCOM Serial Debug Assistant V2.0: An efficient and easy-to-use serial communication tool. Download Link
- SSCOM3.2 Serial Assistant: Designed for embedded development, IoT communication, and daily serial debugging. Download from Project Repository
General Operation Steps
- Hardware Connection: Connect the sensor to the host (computer) via the RainbowLink USB Protocol Converter. Switch the sensor's communication mode to UART and address to 0x47.
- Parameter Configuration: Set the following parameters in the serial debug tool (must match the sensor's configuration):
- Baud Rate: 9600 (default)
- Data Bits: 8 bits
- Stop Bits: 1 bit
- Parity: None
- Send Command: Enter the hexadecimal command in the "Transmit Area" of the debug tool, check "Hex Send", and click Send.
Example 1: Read Pressure Value (Input Register Read Operation)
Function: Read the current pressure value detected by the sensor via the Modbus RTU protocol.
Transmit Command & Parsing
| Field Name | Hex Value | Description |
|---|---|---|
| Device Address | 47 | Default UART address of the sensor (0x47) |
| Function Code | 04 | Read Input Registers (fixed command) |
| Starting Register Address | 00 26 | Lowest significant register address for pressure data |
| Number of Registers | 00 03 | Read 3 consecutive registers |
| CRC Check | 5F 66 | Command checksum (ensures transmission integrity) |
Complete Transmit Command: 47 04 00 26 00 03 5F 66
Response Data & Parsing
After receiving the command, the sensor returns pressure data. Example response:
| Field Name | Hex Value | Description |
|---|---|---|
| Device Address | 47 | Matches the device address in the transmit command |
| Function Code | 04 | Confirms execution of "Read Input Registers" operation |
| Number of Bytes | 06 | Total number of returned data bytes (6 bytes) |
| Read Data | 00 05 00 FD 00 5B | Raw pressure data (requires conversion to standard pressure unit (Pa) using the formula below) |
| CRC Check | 66 FB | Checksum of the response data |
Complete Response Data: 47 04 06 00 05 00 FD 00 5B 66 FB
Data Conversion Principle
The complete pressure data in Modbus registers consists of 3 Input Registers (address range: 0x0026-0x0028). Since data must be read starting from the lowest significant register, the starting address in the command is set to 0x0026, and the response data follows the same order (from least significant to most significant).
- Response data breakdown:
- "00 05": Least Significant Byte (LSB)
- "00 FD": Middle Significant Byte
- "00 5B": Most Significant Byte (MSB)
- Reassemble the bytes in MSB-to-LSB order: 00 5B 00 FD 00 05
- Convert hexadecimal to decimal: 6028549
- Pressure calculation formula: Pressure (Pa) = Raw Data / 2⁶
- Result: Pressure = 6028549 / 64 = 94196 (Pa)
Schematic Diagram:
Example 2: Modify Module Baud Rate (Holding Register Write Operation)
Function: Modify the sensor's UART baud rate via the Modbus RTU protocol (default: 9600, customizable).
Transmit Command & Parsing
| Field Name | Hex Value | Description |
|---|---|---|
| Device Address | 47 | Default address of the sensor (0x47) |
| Function Code | 06 | Write Single Holding Register (fixed command) |
| Starting Register Address | 00 01 | Register address corresponding to baud rate configuration |
| Data to Write | 00 08 | Corresponding to 115200 bps (see Register Table for value-baud rate mapping) |
| CRC Check | D7 6A | Command checksum |
Complete Transmit Command: 47 06 00 01 00 08 D7 6A
Complete Response Data: 47 06 00 01 00 08 D7 6A
Notes
- If the response data matches the transmit command, the baud rate modification request has been accepted by the device.
- The new baud rate takes effect only after powering off and restarting the sensor.
- After restart, update the serial debug tool's baud rate to 115200; otherwise, communication will fail.
Schematic Diagram:
Was this article helpful?