1  # Simple demo of the SI5351 clock generator.
 2  # This is like the Arduino library example:
 3  #   https://github.com/adafruit/Adafruit_Si5351_Library/blob/master/examples/si5351/si5351.ino
 4  # Which will configure the chip with:
 5  #  - PLL A at 900mhz
 6  #  - PLL B at 616.66667mhz
 7  #  - Clock 0 at 112.5mhz, using PLL A as a source divided by 8
 8  #  - Clock 1 at 13.553115mhz, using PLL B as a source divided by 45.5
 9  #  - Clock 2 at 10.76khz, using PLL B as a source divided by 900 and further
10  #    divided with an R divider of 64.
11  import board
12  import busio
13  
14  import adafruit_si5351
15  
16  
17  # Initialize I2C bus.
18  i2c = busio.I2C(board.SCL, board.SDA)
19  
20  # Initialize SI5351.
21  si5351 = adafruit_si5351.SI5351(i2c)
22  # Alternatively you can specify the I2C address if it has been changed:
23  # si5351 = adafruit_si5351.SI5351(i2c, address=0x61)
24  
25  # Now configue the PLLs and clock outputs.
26  # The PLLs can be configured with a multiplier and division of the on-board
27  # 25mhz reference crystal.  For example configure PLL A to 900mhz by multiplying
28  # by 36.  This uses an integer multiplier which is more accurate over time
29  # but allows less of a range of frequencies compared to a fractional
30  # multiplier shown next.
31  si5351.pll_a.configure_integer(36)  # Multiply 25mhz by 36
32  print("PLL A frequency: {0}mhz".format(si5351.pll_a.frequency / 1000000))
33  
34  # And next configure PLL B to 616.6667mhz by multiplying 25mhz by 24.667 using
35  # the fractional multiplier configuration.  Notice you specify the integer
36  # multiplier and then a numerator and denominator as separate values, i.e.
37  # numerator 2 and denominator 3 means 2/3 or 0.667.  This fractional
38  # configuration is susceptible to some jitter over time but can set a larger
39  # range of frequencies.
40  si5351.pll_b.configure_fractional(24, 2, 3)  # Multiply 25mhz by 24.667 (24 2/3)
41  print("PLL B frequency: {0}mhz".format(si5351.pll_b.frequency / 1000000))
42  
43  # Now configure the clock outputs.  Each is driven by a PLL frequency as input
44  # and then further divides that down to a specific frequency.
45  # Configure clock 0 output to be driven by PLL A divided by 8, so an output
46  # of 112.5mhz (900mhz / 8).  Again this uses the most precise integer division
47  # but can't set as wide a range of values.
48  si5351.clock_0.configure_integer(si5351.pll_a, 8)
49  print("Clock 0: {0}mhz".format(si5351.clock_0.frequency / 1000000))
50  
51  # Next configure clock 1 to be driven by PLL B divided by 45.5 to get
52  # 13.5531mhz (616.6667mhz / 45.5).  This uses fractional division and again
53  # notice the numerator and denominator are explicitly specified.  This is less
54  # precise but allows a large range of frequencies.
55  si5351.clock_1.configure_fractional(si5351.pll_b, 45, 1, 2)  # Divide by 45.5 (45 1/2)
56  print("Clock 1: {0}mhz".format(si5351.clock_1.frequency / 1000000))
57  
58  # Finally configure clock 2 to be driven by PLL B divided once by 900 to get
59  # down to 685.15 khz and then further divided by a special R divider that
60  # divides 685.15 khz by 64 to get a final output of 10.706khz.
61  si5351.clock_2.configure_integer(si5351.pll_b, 900)
62  # Set the R divider, this can be a value of:
63  #  - R_DIV_1: divider of 1
64  #  - R_DIV_2: divider of 2
65  #  - R_DIV_4: divider of 4
66  #  - R_DIV_8: divider of 8
67  #  - R_DIV_16: divider of 16
68  #  - R_DIV_32: divider of 32
69  #  - R_DIV_64: divider of 64
70  #  - R_DIV_128: divider of 128
71  si5351.clock_2.r_divider = adafruit_si5351.R_DIV_64
72  print("Clock 2: {0}khz".format(si5351.clock_2.frequency / 1000))
73  
74  # After configuring PLLs and clocks, enable the outputs.
75  si5351.outputs_enabled = True
76  # You can disable them by setting false.