# Modbus Protocol This device communicates using the Modbus RTU protocol over the RS-485 standard. ## Device Address This device's preconfigured user-definable address is **0x15**. Users can change the address using the holding registers. ## Modbus Function Codes The following Modbus function codes are functional with this device.
Command RegisterFunctionDescriptionBytesFunctionLength (Bytes)Description
0x03Read holding registersReturns configuration parameters2Read holding registers2Stores last read measurements
0x04Read input registersReturns measured readings and statistics2Read input registernull
0x06Write single registerWrites a single configuration parameter2Write single keep registernull
0x10Write multiple registersWrites multiple configuration parameters2 x NWrite multiple keep registernull
## Device Registers The following registers are available with this device.
Register TypeRegister AddressDescriptionBytes
Input Register (R)0x0001Air Quality Index (Actual)2
Input Register (R)0x0002Air Quality Index (Average)2
Input Register (R)0x0003Air Quality Index (Min)2
Input Register (R)0x0004Air Quality Index (Max)2
Input Register (R)0x0005Air Quality Index (Std. Dev.)2
Input Register (R)0x0006VOC Index (Actual)2
Input Register (R)0x0007VOC Index (Average)2
Input Register (R)0x0008VOC Index (Min)2
Input Register (R)0x0009VOC Index (Max)2
Input Register (R)0x000AVOC Index (Std. Dev.)2
Input Register (R)0x000BNOx Index (Actual)2
Input Register (R)0x000CNOx Index (Average)2
Input Register (R)0x000DNOx Index (Min)2
Input Register (R)0x000ENOx Index (Max)2
Input Register (R)0x000FNOx Index (Std. Dev.)2
Input Register (R)0x0010PM 1.0 (Actual)2
Input Register (R)0x0011PM 1.0 (Average)2
Input Register (R)0x0012PM 1.0 (Min)2
Input Register (R)0x0013PM 1.0 (Max)2
Input Register (R)0x0014PM 1.0 (Std. Dev.)2
Input Register (R)0x0015PM 2.5 (Actual)2
Input Register (R)0x0016PM 2.5 (Average)2
Input Register (R)0x0017PM 2.5 (Min)2
Input Register (R)0x0018PM 2.5 (Max)2
Input Register (R)0x0019PM 2.5 (Std. Dev.)2
Input Register (R)0x001APM 4.0 (Actual)2
Input Register (R)0x001BPM 4.0 (Average)2
Input Register (R)0x001CPM 4.0 (Min)2
Input Register (R)0x001DPM 4.0 (Max)2
Input Register (R)0x001EPM 4.0 (Std. Dev.)2
Input Register (R)0x001FPM 10 (Actual)2
Input Register (R)0x0020PM 10 (Average)2
Input Register (R)0x0021PM 10 (Min)2
Input Register (R)0x0022PM 10 (Max)2
Input Register (R)0x0023PM 10 (Std. Dev.)2
Input Register (R)0x0024CO2 (Actual)2
Input Register (R)0x0025CO2 (Average)2
Input Register (R)0x0026CO2 (Min)2
Input Register (R)0x0027CO2 (Max)2
Input Register (R)0x0028CO2 (Std. Dev.)2
Input Register (R)0x0029Device Pitch (Actual)2
Input Register (R)0x002ADevice Roll (Actual)2
Input Register (R)0x002BDevice Temperature2
Holding Register (R/W)0x0101Device Address2
Holding Register (R/W)0x0102Baud Rate2
Holding Register (R/W)0x0103Statistics Period (Secs)2
Holding Register (R/W)0x0104IMU Correction (Pitch)2
Holding Register (R/W)0x0105IMU Correction (Roll)2
## Communication Syntax ### Reading sensor data The host device can read one or more sensor data by calling the starting register address. **Request from the host:** Device address \[1 Byte] + Function code (0x04) \[1 Byte] + Input register start address \[2 Bytes MSB first] + Requested register length \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] **Response from the device:** Device address \[1 Byte] + Function code (0x04) \[1 Byte] + Response register length in Bytes \[1 Byte] + Register 1 \[2 Bytes MSB first] + Register N \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] ### Reading configuration register The host device can read one or more configuration registers by calling the starting register address. **Request from the host:** Device address \[1 Byte] + Function code (0x03) \[1 Byte] + Holding register start address \[2 Bytes MSB first] + Requested register length \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] **Response from the device:** Device address \[1 Byte] + Function code (0x03) \[1 Byte] + Response register length in Bytes \[1 Byte], Register 1 \[2 Bytes MSB first] + Register N \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] ### Writing single configuration register The host device can write one configuration register. **Command from the host:** Device address \[1 Byte] + Function code (0x06) \[1 Byte] + Holding register address \[2 Bytes MSB first] + Value to be set \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] **Response from the device:** Device address \[1 Byte] + Function code (0x06) \[1 Byte] + Holding register address \[1 Byte] + Value set \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] ### Writing multiple configuration registers The host device can write multiple configuration registers. **Command from the host:** Device address \[1 Byte] + Function code (0x10) \[1 Byte] + Holding register start address \[2 Bytes MSB first] + Requested register length \[2 Bytes] + Configuration values length in Bytes \[1 Byte] + Value to be set 1 \[2 Bytes MSB first] + Value to be set N \[2 Bytes MSB first] + CRC \[2 Bytes MSB first] **Response from the device:** Device address \[1 Byte] + Function code (0x10) \[1 Byte] + Holding register start address \[1 Byte], Value set \[2 Bytes MSB first], CRC \[2 Bytes MSB first] --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.evolion.io/hw/environmental-monitoring/air-quality-sensor/modbus-protocol.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.