Datasheet

adafruit_si5351.mpy

adafruit_bus_device

Before continuing make sure your board's lib folder or root filesystem has

the adafruit_si5351.mpy, and adafruit_bus_device files and folders copied over.

Next connect to the board's serial REPL (https://adafru.it/Awz) so you are at the CircuitPython >>> prompt.

Python Installation of SI5351 Library

You'll need to install the Adafruit_Blinka library that provides the CircuitPython support in Python. This may also

require enabling I2C on your platform and verifying you are running Python 3. Since each platform is a little different,

and Linux changes often, please visit the CircuitPython on Linux guide to get your computer

ready (https://adafru.it/BSN)!

Once that's done, from your command line run the following command:

sudo pip3 install adafruit-circuitpython-si5351

If your default Python is version 3 you may need to run 'pip' instead. Just make sure you aren't trying to use

CircuitPython on Python 2.x, it isn't supported!

CircuitPython & Python Usage

To demonstrate the usage of the sensor we'll initialize it and control the clocks from the board's Python REPL. Run the

following code to import the necessary modules and initialize the I2C connection with the sensor:

Now you're ready to configure the PLLs and clock outputs on the chip. The SI5351 is somewhat complex and allows

quite many configurations to balance the accuracy and range of clock output values. You'll want to review the

datasheet (https://adafru.it/C5E) to understand the capabilities and features of the chip.

Configure Phase Lock Loops

First you'll need to configure one of the two PLLs (phase-locked loops, special hardware that can 'multiply' the 25 MHz

crystal to much faster speeds) which will be used as the source of any of the clock outputs. The Si5351 object has two

PLL objects you can manipulate:

pll_a This is the PLL A hardware on the chip.

pll_b This is the PLL B hardware on the chip.

You can configure each PLL's multiplier by calling the configure_integer or configure_fractional function. The integer

configuration lets you set an integer multiplier for the 25 MHz base crystal frequency. This is the most accurate way to

control frequency but you can only set integer multiples. For example to set PLL A to 500 MHz you'd set an integer

multiplier of 20 (25 MHz * 20 = 500 MHz):

import board

import busio

import adafruit_si5351

i2c = busio.I2C(board.SCL, board.SDA)

si5351 = adafruit_si5351.SI5351(i2c)

si5351.pll_a.configure_integer(20)