RF / Hope RF / RFM75-S2

General Description

RFM75 is a GFSK transceiver operating in the world wide ISM frequency band at 2400-2483.5 MHz.Burst mode transmission and up to 2Mbps air data rate make them suitable for applications requiring ultra low power consumption. The embedded packet processing engines enable their full operation with a very simple MCU as a radio system. Auto re-transmission and auto acknowledge give reliable link without any MCU interference. 
RFM75 operates in TDD mode, either as a transmitter or as a receiver.
The RF channel frequency determines the center of the channel used by RFM75. The frequency is set by the RF_CH register in register bank 0 according to the following formula: F0= 2400 + RF_CH (MHz). The resolution of the RF channel frequency is 1MHz.
A transmitter and a receiver must be programmed with the same RF channel frequency to be able to communicate with each other. The output power of RFM75 is set by the RF_PWR bits in the RF_SETUP register. 
Demodulation is done with embedded data slicer and bit recovery logic. The air data rate can be programmed to 250Kbps, 1Mbps or 2Mbps by RF_DR_HIGH and RF_DR_LOW register. A transmitter and a receiver must be programmed with the same setting.
In the following chapters, all registers are in register bank 0 except with explicit claim.


  • 2400-2483.5 MHz ISM band operation
  • Support 250Kbps, 1Mbps and 2 Mbps airdata rate
  • Programmable output power
  • Tolerate +/- 60ppm 16 MHz crystal
  • Variable payload length from 1 to 32bytes
  • Automatic packet processing
  • 6 data pipes for 1:6 star networks
  • 1.9V to 3.6V power supply
  • 4-pin SPI interface with maximum 8 MHz clock rate
  • 20-pin 4x4mm QFN package


  • Wireless PC peripherals
  • Wireless gamepads
  • Wireless audio
  • Remote controls
  • Home automation
  • Toys
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