This driver follows PyroScience FDO2-G2, document version v5 (03/2026), §4 Communication Interface.

Electrical and framing

3.0 V UART levels (absolute maximum 3.3 V on IO).
8N1, no handshake.
Default baud after power-up: 19200 (1200 … 115200 programmable via #BAUD; not wrapped in this driver yet).
Allow **~1 s** after power-up before commands.
Host commands end with carriage return (0x0D), or CR+LF (0x0D 0x0A).
Device responses end with CR only.
If CRC is enabled (#CRCE 1), each response ends with : <decimal CRC16> before CR. The driver strips that suffix before tokenizing.

Implemented commands

Command	Response shape	Driver API
`#VERS`	`#VERS D N R S`	`ReadVersion()`
`#IDNR`	`#IDNR N` (64-bit decimal)	`ReadUniqueId()`
`#MOXY`	`#MOXY O T S`	`MeasureMoxy()`
`#MRAW`	`#MRAW O T S D I A P H`	`MeasureMraw()`
`#LOGO`	`#LOGO`	`FlashLogo()`

Numeric decoding

O — pO₂ in 10⁻³ hPa → p_o2_hpa = O × 10⁻³.
T — temperature in m°C → temp_c = T × 10⁻³.
S — unsigned 32-bit status. Normal operation: S = 0 or 1 only.
**#MRAW** extras: D in millidegrees; I, A in µV → mV with ×10⁻³; P in µbar → mbar with ×10⁻⁶; H in mRH → RH with ×10⁻³.

Constants for individual status bits live in fdo2::moxy_status in fdo2_types.hpp.

Volume % O₂

When pressure at the sensing membrane matches the vent / back-side pressure represented by P in #MRAW:

O₂ = 100 × pO₂ [hPa] / p_air [hPa] (mbar ≈ hPa for this ratio per data sheet §2).

Use VolumePercentO2(p_o2_hpa, pressure_mbar).

Errors

Responses beginning with #ERRO followed by signed E (Table 1, §4.4). When DriverResult::error == DeviceError, read Driver::LastDeviceErrorCode().

Out of scope in this driver

Flash-writing commands (#CALO, #CAHI, #CRCE, #SETM, #BCST, #BAUD, #WRUM, …) are not exposed: they consume flash endurance (~20k cycles total) and require stable power during programming (data sheet warning).

Next: Hardware setup →