FDO2-G2 UART protocol

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 ` : ` 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 m%RH → %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 →