Datasheet

50 stdio_init_all();
51
52 pio_spi_inst_t spi = {
53 .pio = pio0,
54 .sm = 0
55 };
56 float clkdiv = 31.25f; // 1 MHz @ 125 clk_sys
57 uint cpha0_prog_offs = pio_add_program(spi.pio, &spi_cpha0_program);
58 uint cpha1_prog_offs = pio_add_program(spi.pio, &spi_cpha1_program);
59
60 for (int cpha = 0; cpha <= 1; ++cpha) {
61 for (int cpol = 0; cpol <= 1; ++cpol) {
62 printf("CPHA = %d, CPOL = %d\n", cpha, cpol);
63 pio_spi_init(spi.pio, spi.sm,
64 cpha ? cpha1_prog_offs : cpha0_prog_offs,
65 8, // 8 bits per SPI frame
66 clkdiv,
67 cpha,
68 cpol,
69 PIN_SCK,
70 PIN_MOSI,
71 PIN_MISO
72 );
73 test(&spi);
74 sleep_ms(10);
75 }
76 }
77 }
3.6.2. WS2812 LEDs
WS2812 LEDs are driven by a proprietary pulse-width serial format, with a wide positive pulse representing a "1" bit, and
narrow positive pulse a "0". Each LED has a serial input and a serial output; LEDs are connected in a chain, with each
serial input connected to the previous LED’s serial output.
Symbol
Output
1 0 0 1 Latch
Figure 51. WS2812
line format. Wide
positive pulse for 1,
narrow positive pulse
for 0, very long
negative pulse for
latch enable
LEDs consume 24 bits of pixel data, then pass any additional input data on to their output. In this way a single serial
burst can individually program the colour of each LED in a chain. A long negative pulse latches the pixel data into the
LEDs.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/ws2812/ws2812.pio Lines 7 - 26
Ê7 .program ws2812
Ê8 .side_set 1
Ê9
10 .define public T1 2
11 .define public T2 5
12 .define public T3 3
13
14 .lang_opt python sideset_init = pico.PIO.OUT_HIGH
15 .lang_opt python out_init = pico.PIO.OUT_HIGH
16 .lang_opt python out_shiftdir = 1
17
18 .wrap_target
19 bitloop:
20 out x, 1 side 0 [T3 - 1] ; Side-set still takes place when instruction stalls
RP2040 Datasheet
3.6. Examples 367