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SEN07xx Intelligent Gas Sensor: Modbus RTU Register Map

This document describes the register map using the columns "type, address, name, access, typical value, and description." Specification source: Arduino library DFRobot_IntelligentGasSensor V1.0.0 (src/DFRobot_IntelligentGasSensor.h). The definitions match the Modbus RTU slave behavior of the SEN07xx sensors.

Some generic Modbus tables define input register 0x0000 as VID and 0x0001 as PID. For this product family, 0x0000 is PID and 0x0001 is VID.

Default link settings: 9600 8N1, slave address 1 (valid range: 1 to 247). The sensor exposes RS-485 A/B terminals. Connect a 3.3 V host such as an ESP32 through a UART-to-RS-485 converter.

1. Function Codes

Type Function code Description
Input registers 0x04 Read-only; each register is 16 bits
Holding registers 0x03 read / 0x06 single write / 0x10 multiple write Configuration and COMMIT

32-bit concentration: combine 0x0009 (low word) + 0x000A (high word) into an unsigned 32-bit value, with the low word first.

Host-library read lengths (readGasMeasurementData):

API FC 0x04 start address Register count Description
readGasMeasurementData(false) 0x0000 12 (0x0000 to 0x000B) Default; no timestamp
readGasMeasurementData(true) 0x0000 18 (0x0000 to 0x0011) Includes year, month, day, hour, minute, and second

2. Input Registers (FC 0x04)

There are 18 input registers (0x0000 to 0x0011). Their library macro prefix is DFROBOT_IGS_IN_REG_*.

Type Address Name Access Typical value Description
Input 0x0000 PID R 0xC746 RS-485 board (SEN0746); TTL board: 0xC742 (SEN0742)
Input 0x0001 VID R 0x3343 DFRobot
Input 0x0002 Modbus slave address R 1 to 247 Current slave address
Input 0x0003 Reserved 0 R 0 Always reads 0
Input 0x0004 Reserved 1 R 0 Always reads 0
Input 0x0005 Register-map version R 0x0100 DFROBOT_IGS_REGMAP_VERSION
Input 0x0006 Reserved 2 R 0 Always reads 0; not a board-type or RUN/SLEEP field (probe RUN/SLEEP is holding register 0x0005 only)
Input 0x0007 Status R — bit 0 = measurement valid (DFROBOT_IGS_STATUS_VALID_MSK)
Input 0x0008 GAS_CODE R — Gas code; the host library decodes type and unit (see Section 5)
Input 0x0009 Concentration low word R — Low 16 bits of the 32-bit concentration
Input 0x000A Concentration high word R — High 16 bits of the 32-bit concentration
Input 0x000B Decimal places R 0 to 12 Concentration = raw value × 10^−dp; library method getConcentrationFloat()
Input 0x000C Year R 2000 to 2099 May be 0 when no RTC is available
Input 0x000D Month R 1 to 12
Input 0x000E Day R 1 to 31
Input 0x000F Hour R 0 to 23
Input 0x0010 Minute R 0 to 59
Input 0x0011 Second R 0 to 59

3. Holding Registers (FC 0x03 / 0x06 / 0x10)

There are 8 holding registers (0x0000 to 0x0007). Their library macro prefix is DFROBOT_IGS_HOLD_REG_*.

After changing the baud rate, parity, or slave address, write 0xA501 (DFROBOT_IGS_COMMIT_KEY_SAVE_CONFIG) to 0x0007 to COMMIT the shadow configuration to EEPROM. Probe sleep at 0x0005 is not stored in EEPROM and takes effect immediately.

Type Address Name Access Typical value Description
Holding 0x0000 Reserved R/W 0 Always reads 0
Holding 0x0001 Reserved R/W 0 Always reads 0
Holding 0x0002 Reserved R/W 0 Always reads 0
Holding 0x0003 Baud-rate code R/W 3 See the table below. After replying, SEN07xx commonly changes its active baud immediately; the host must call Serial.begin with the new baud before COMMIT (see changeDeviceBaudrate)
Holding 0x0004 Parity / stop bits R/W 0 See the table below; saved together with 0x0003 by COMMIT
Holding 0x0005 Probe sleep R/W 0 0 = RUN, 1 = SLEEP; immediate and not saved; library methods setProbeSleep() / getProbeWorkMode()
Holding 0x0006 Slave address R/W 1 1 to 247; replies using the new address immediately; COMMIT is required for persistence; library method setDeviceAddress()
Holding 0x0007 COMMIT W 0xA501 Save the shadow configuration to EEPROM; library method commitConfiguration()

3.1 Baud-rate Code (0x0003)

Code Baud rate Library macro
1 2400 DFROBOT_IGS_BAUD_CODE_2400
2 4800 DFROBOT_IGS_BAUD_CODE_4800
3 9600 DFROBOT_IGS_BAUD_CODE_9600
4 14400 DFROBOT_IGS_BAUD_CODE_14400
5 19200 DFROBOT_IGS_BAUD_CODE_19200
6 38400 DFROBOT_IGS_BAUD_CODE_38400
7 57600 DFROBOT_IGS_BAUD_CODE_57600
8 115200 DFROBOT_IGS_BAUD_CODE_115200

3.2 Parity / Stop Bits (0x0004)

The lower two bits select parity, and bit 2 selects the number of stop bits, matching the library macros:

Field Value Library macro Meaning
Parity 0 DFROBOT_IGS_PARITY_NONE No parity (N)
Parity 1 DFROBOT_IGS_PARITY_ODD Odd parity (O)
Parity 2 DFROBOT_IGS_PARITY_EVEN Even parity (E)
Stop bits 0 DFROBOT_IGS_STOPBIT_1 1 stop bit
Stop bits 4 (bit 2) DFROBOT_IGS_STOPBIT_2 2 stop bits

The factory default is normally 0 (8N1).

4. Host-library API to Register Mapping

Library API Register range Description
readGasMeasurementData(false) Input 0x0000 to 0x000B FC 0x04, 12 registers
readGasMeasurementData(true) Input 0x0000 to 0x0011 FC 0x04, 18 registers
writeDeviceBaudCode(code) Holding 0x0003 FC 0x06 only; no COMMIT
commitConfiguration() Holding 0x0007 = 0xA501 FC 0x06
setDeviceAddress(addr) Holding 0x0006 + COMMIT
setProbeSleep(sleep) Holding 0x0005 0 = RUN, 1 = SLEEP
setClientSlaveAddr(addr) — Changes only the address used by host requests; does not write a register

5. Host-side GAS_CODE Table (SMX100)

The bus reports only GAS_CODE. The library generates gasType and unit from its internal table. An unknown code is displayed as 0xNN.

GAS_CODE Gas type Default unit
0x01 CH4 %LEL
0x03 H2S ppm
0x04 CO ppm
0x05 O2 %VOL

6. Related Files

Content Path
Host-library header and implementation src/DFRobot_IntelligentGasSensor.{h,cpp}
Library documentation README.md / README_CN.md
Manual Modbus test frames (Chinese) docs/MANUAL_TEST_RS485_MODBUS_CN.md
Examples examples/readGasRS485, examples/changeDeviceBaudrate, and others

Document version: V1.0.0, 2026-05-21. Aligned with the DFRobot_IntelligentGasSensor library.