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RC-S2LP Wireless M-Bus Transceiver#

Overview, Hardware Connection, and Test Procedure#

Introduction#

The RC-S2LP is a sub-GHz RF transceiver module based on the STMicroelectronics S2-LP radio IC. It is commonly used in Wireless M-Bus (wM-Bus), smart metering, and low-power IoT gateway applications operating in the 868 MHz ISM band.

In the S0 board, the RC-S2LP is responsible for receiving and transmitting Wireless M-Bus frames from devices such as heat meters, water meters, and gas meters.

What the RC-S2LP Module Is Used For#

The RC-S2LP enables:

  • Wireless M-Bus communication (T1, T2, C1, C2 modes)
  • Sub-GHz long-range communication
  • Low-power RF reception from battery-powered meters
  • Gateway-to-meter RF communication
  • Custom proprietary RF protocols

Typical applications include:

  • Smart utility meters
  • IoT gateways
  • Industrial telemetry
  • Building automation systems

Key Specifications#

Feature Description
RF IC STMicroelectronics S2-LP
Frequency Band 868 MHz ISM band
Modulation 2-FSK, GFSK, OOK, MSK
Data Rate Up to 500 kbps
Output Power Up to +14 dBm
Sensitivity Down to −130 dBm (mode-dependent)
Interface SPI
Operating Voltage 1.8 V – 3.6 V
Low-Power Modes Sleep, Standby

Hardware Connection#

The RC-S2LP communicates with the host MCU using SPI and several control signals.

Required Signals#

Signal Description
MOSI SPI Master Out
MISO SPI Master In
SCK SPI Clock
CS SPI Chip Select
VCC 3.3 V supply
GND Ground
RF 868 MHz antenna

Example Connection (ESP32)#

RC-S2LP Pin MCU Pin
MOSI SPI MOSI
MISO SPI MISO
SCK SPI SCK
CS GPIO
VCC 3.3V
GND GND

⚠️ Ensure a proper 868 MHz antenna is connected before transmitting.

Software Test Procedure#

Test Objective#

The test verifies that:

  • The RC-S2LP is powered correctly
  • SPI communication is functional
  • Registers can be read and written
  • RF transmission and reception work

SPI Communication Test#

Example code for this test can be found in the Wireless MBUS test code