UART Protocol

F103 ↔ EMW3165 UART Protocol

The original F103 sensor/display controller communicates with the EMW3165's STM32F411 over USART2 at 115200 8N1. Rewair keeps this interface so the stock sensor and display firmware remain in service.

Frame format

*CMDLLLLLLLL\0field\0value\0...#

• CMD is a four-byte ASCII token.
• LLLLLLLL is the eight-digit uppercase hexadecimal payload length.
• The payload is a sequence of NUL-separated fields.
• # terminates the frame.

The receiver validates the header, declared length, and trailer before handing a frame to the bridge.

Commands used by Rewair

Current firmware sends:

Token	Purpose
NETW	Network state, RSSI, address, and MAC
TINF	Timezone and daylight-saving transition data derived from the saved POSIX rule
TIME	Current wall-clock time
DISP	Display mode
SCOR	Calculated score and sensor-index display data

Current firmware handles these incoming frames explicitly:

Token	Purpose
SENS	Sensor readings used for status, scoring, and MQTT
REDY	Sensor-board ready indication
RUNN	Running/liveness indication
BTST	Boot/self-test state
TEST	Test lifecycle state
NETD	Network-down request/state
NETR	Network-restart request/state

Additional observed vocabulary

The stock firmware contains more tokens than Rewair currently needs. Their names and likely roles are retained here without claiming complete semantics:

• Display and interaction: SLEP, NOTI, SUND, KNCK, ALRM, TUTO, MESG, LEDS
• Identity and status: VERS, SCCD, DVID, MACA, SSID, WVER, SVER, WLOG, WSTA
• Update and control: HASH, UPGR, DOWN, FNOW, FDEF, DEBG, BOOT
• Test lifecycle: TEND

Some tokens may be bidirectional request/response pairs. Direction and payload meaning should be treated as unknown until observed on the wire or confirmed in the F103 firmware.

Confirmed display experiments

• DISP mode clock shows the clock.
• DISP mode default blanked the display on the tested unit.
• MESG message hello timeout 5 uses message and timeout field names.
• LEDS color white blink 0 produces a steady white LED.
• SCOR requires the empty index and sensor separators used by the bridge.

Open questions

• Which boot-context frames are mandatory before the F103 starts SENS?
• Whether SCOR is ever emitted spontaneously by the F103.
• Whether DOWN refers to network state, firmware download state, or both.
• Which unimplemented tokens are required to clear any F103-side error state.