Datasheet

39 sm_config_set_sideset_pins(&c, pin_tx);
40
41 // We only need TX, so get an 8-deep FIFO!
42 sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);
43
44 // SM transmits 1 bit per 8 execution cycles.
45 float div = (float)clock_get_hz(clk_sys) / (8 * baud);
46 sm_config_set_clkdiv(&c, div);
47
48 pio_sm_init(pio, sm, offset, &c);
49 pio_sm_set_enabled(pio, sm, true);
50 }
The state machine is configured to shift right in out instructions, because UARTs typically send data LSB-first. Once
configured, the state machine will print any characters pushed to the TX FIFO.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/uart_tx/uart_tx.pio Lines 52 - 54
52 static inline void uart_tx_program_putc(PIO pio, uint sm, char c) {
53 pio_sm_put_blocking(pio, sm, (uint32_t)c);
54 }
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/uart_tx/uart_tx.pio Lines 56 - 59
56 static inline void uart_tx_program_puts(PIO pio, uint sm, const char *s) {
57 while (*s)
58 uart_tx_program_putc(pio, sm, *s++);
59 }
The example program in the SDK will configure one PIO state machine as a UART TX peripheral, and use it to print a
message on GPIO 0 at 115200 baud once per second.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/uart_tx/uart_tx.c Lines 1 - 27
Ê1 /**
Ê2 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
Ê3 *
Ê4 * SPDX-License-Identifier: BSD-3-Clause
Ê5 */
Ê6
Ê7 #include "pico/stdlib.h"
Ê8 #include "hardware/pio.h"
Ê9 #include "uart_tx.pio.h"
10
11 int main() {
12 // We're going to use PIO to print "Hello, world!" on the same GPIO which we
13 // normally attach UART0 to.
14 const uint PIN_TX = 0;
15 // This is the same as the default UART baud rate on Pico
16 const uint SERIAL_BAUD = 115200;
17
18 PIO pio = pio0;
19 uint sm = 0;
20 uint offset = pio_add_program(pio, &uart_tx_program);
21 uart_tx_program_init(pio, sm, offset, PIN_TX, SERIAL_BAUD);
22
23 while (true) {
24 uart_tx_program_puts(pio, sm, "Hello, world! (from PIO!)\n");
RP2040 Datasheet
3.6. Examples 370