README.md

PU2REO_Si570

Library for the Si570 10 MHz to 1.4 GHz I2C programmable XO/VCXO, in the Arduino environment.

The Si570 XO/Si571 VCXO utilizes Skyworks Solutions’ advanced DSPLL® circuitry to provide a low-jitter clock at any frequency. The Si570/Si571 are user-programmable to any output frequency from 10 to 945 MHz and select frequencies to 1400 MHz with <1 ppb resolution. The device is programmed via an I2C serial interface. Unlike traditional XO/VCXOs where a different crystal is required for each output frequency, the Si57x uses one fixed-frequency crystal and a DSPLL clock synthesis IC to provide any-frequency operation. This IC-based approach allows the crystal resonator to provide exceptional frequency stability and reliability. In addition, DSPLL clock synthesis provides superior supply noise rejection, simplifying the task of generating low-jitter clocks in noisy environments typically found in communication systems.

Public Methods

PU2REO_Si570(void);
void      Init(void);
void      Reset(void);
float     Get_Frequency(void);
float     Get_RFreq(void);
uint16_t  Get_N1(void);
int16_t   Get_HSdiv(void);
void      Get_Registers(void);
int16_t   Set_Frequency(float currentFrequency);
int16_t   Set_Frequency_Small_Change(float currentFrequency);
int16_t   Set_Frequency_Large_Change(float currentFrequency);
uint8_t   SetBits(uint8_t original, uint8_t reset_mask, uint8_t new_val);
void      Read(uint8_t init_reg, uint8_t *buffer, uint8_t size);
void      Write(uint8_t *buffer, uint8_t size);

What sets this library apart from the others?

• The frequency of the internal crystal oscillator (Si570_Data.FXtal) is calculated based on the initial frequency output after an internal reset of the Si570, eliminating the need for corrections. In some versions I have seen, you have to enter this variable manually and therefore, the accuracy of the output frequency decreases.

  void PU2REO_Si570::Reset(void)
  {
      // writes command to the Si570
      CmdBuffer[0] = SI570_REG_135;  // Position
      CmdBuffer[1] = 0x01;           // Reset command
      this->Write(CmdBuffer, 2);     // Send command string
  
      // get registers and calculate current frequency
      this->Get_Registers();
      Si570_Data.FXtal = (FOUT_START_UP * Si570_Data.N1 * Si570_Data.HSDiv) / Si570_Data.RFreq; //MHz
      Si570_Data.CurrentFreq = FOUT_START_UP;
      Si570_Data.CurrentRFreq = Si570_Data.RFreq;
  }

• Possibility of reading/writing any of the Si570 internal registers at any time.
• Perform small changes on the output frequency (inside de window of 3500ppm) on the fly just recalculating RFREQ register.

Very important notice:

Si570 runs on 3.3V only. It will be necessary a voltage level converter to run it powered by Arduino 5V bus. A cheap and useful one is displayed bellow for reference:

A wave of hand to:

Gerrit Polder, PA3BYA, the one who made it first for mbed around 2010.