Universal Asynchronous Receiver/Transmitter (UART)
Overview
A Universal Asynchronous Receiver/Transmitter (UART) is a hardware feature that handles communication (i.e., timing requirements and data framing) using widely-adopted asynchronous serial communication interfaces, such as RS232, RS422, RS485. A UART provides a widely adopted and cheap method to realize full-duplex or half-duplex data exchange among different devices.
The ESP32-C3 chip has two UART controllers (UART0 and UART1), each featuring an identical set of registers to simplify programming and for more flexibility.
Each UART controller is independently configurable with parameters such as baud rate, data bit length, bit ordering, number of stop bits, parity bit etc. All the controllers are compatible with UART-enabled devices from various manufacturers and can also support Infrared Data Association protocols (IrDA).
Functional Overview
The following overview describes how to establish communication between an ESP32-C3 and other UART devices using the functions and data types of the UART driver. The overview reflects a typical programming workflow and is broken down into the sections provided below:
Setting Communication Parameters - Setting baud rate, data bits, stop bits, etc.
Setting Communication Pins - Assigning pins for connection to a device.
Driver Installation - Allocating ESP32-C3’s resources for the UART driver.
Running UART Communication - Sending / receiving data
Using Interrupts - Triggering interrupts on specific communication events
Deleting a Driver - Freeing allocated resources if a UART communication is no longer required
Steps 1 to 3 comprise the configuration stage. Step 4 is where the UART starts operating. Steps 5 and 6 are optional.
The UART driver’s functions identify each of the UART controllers using uart_port_t. This identification is needed for all the following function calls.
Setting Communication Parameters
UART communication parameters can be configured all in a single step or individually in multiple steps.
Single Step
Call the function uart_param_config() and pass to it a uart_config_t structure. The uart_config_t structure should contain all the required parameters. See the example below.
const uart_port_t uart_num = UART_NUM_1;
uart_config_t uart_config = {
.baud_rate = 115200,
.data_bits = UART_DATA_8_BITS,
.parity = UART_PARITY_DISABLE,
.stop_bits = UART_STOP_BITS_1,
.flow_ctrl = UART_HW_FLOWCTRL_CTS_RTS,
.rx_flow_ctrl_thresh = 122,
};
// Configure UART parameters
ESP_ERROR_CHECK(uart_param_config(uart_num, &uart_config));
For more information on how to configure the hardware flow control options, please refer to peripherals/uart/uart_echo.
Multiple Steps
Configure specific parameters individually by calling a dedicated function from the table given below. These functions are also useful if re-configuring a single parameter.
Parameter to Configure |
Function |
|---|---|
Baud rate |
|
Number of transmitted bits |
|
Parity control |
|
Number of stop bits |
|
Hardware flow control mode |
|
Communication mode |
|
Each of the above functions has a _get_ counterpart to check the currently set value. For example, to check the current baud rate value, call uart_get_baudrate().
Setting Communication Pins
After setting communication parameters, configure the physical GPIO pins to which the other UART device will be connected. For this, call the function uart_set_pin() and specify the GPIO pin numbers to which the driver should route the Tx, Rx, RTS, and CTS signals. If you want to keep a currently allocated pin number for a specific signal, pass the macro UART_PIN_NO_CHANGE.
The same macro should be specified for pins that will not be used.
// Set UART pins(TX: IO4, RX: IO5, RTS: IO18, CTS: IO19)
ESP_ERROR_CHECK(uart_set_pin(UART_NUM_1, 4, 5, 18, 19));
Driver Installation
Once the communication pins are set, install the driver by calling uart_driver_install() and specify the following parameters:
Size of Tx ring buffer
Size of Rx ring buffer
Event queue handle and size
Flags to allocate an interrupt
The function will allocate the required internal resources for the UART driver.
// Setup UART buffered IO with event queue
const int uart_buffer_size = (1024 * 2);
QueueHandle_t uart_queue;
// Install UART driver using an event queue here
ESP_ERROR_CHECK(uart_driver_install(UART_NUM_1, uart_buffer_size, \
uart_buffer_size, 10, &uart_queue, 0));
Once this step is complete, you can connect the external UART device and check the communication.
Running UART Communication
Serial communication is controlled by each UART controller’s finite state machine (FSM).
The process of sending data involves the following steps:
Write data into Tx FIFO buffer
FSM serializes the data
FSM sends the data out
The process of receiving data is similar, but the steps are reversed:
FSM processes an incoming serial stream and parallelizes it
FSM writes the data into Rx FIFO buffer
Read the data from Rx FIFO buffer
Therefore, an application will be limited to writing and reading data from a respective buffer using uart_write_bytes() and uart_read_bytes() respectively, and the FSM will do the rest.
Transmitting
After preparing the data for transmission, call the function uart_write_bytes() and pass the data buffer’s address and data length to it. The function will copy the data to the Tx ring buffer (either immediately or after enough space is available), and then exit. When there is free space in the Tx FIFO buffer, an interrupt service routine (ISR) moves the data from the Tx ring buffer to the Tx FIFO buffer in the background. The code below demonstrates the use of this function.
// Write data to UART.
char* test_str = "This is a test string.\n";
uart_write_bytes(uart_num, (const char*)test_str, strlen(test_str));
The function uart_write_bytes_with_break() is similar to uart_write_bytes() but adds a serial break signal at the end of the transmission. A ‘serial break signal’ means holding the Tx line low for a period longer than one data frame.
// Write data to UART, end with a break signal.
uart_write_bytes_with_break(uart_num, "test break\n",strlen("test break\n"), 100);
Another function for writing data to the Tx FIFO buffer is uart_tx_chars(). Unlike uart_write_bytes(), this function will not block until space is available. Instead, it will write all data which can immediately fit into the hardware Tx FIFO, and then return the number of bytes that were written.
There is a ‘companion’ function uart_wait_tx_done() that monitors the status of the Tx FIFO buffer and returns once it is empty.
// Wait for packet to be sent
const uart_port_t uart_num = UART_NUM_1;
ESP_ERROR_CHECK(uart_wait_tx_done(uart_num, 100)); // wait timeout is 100 RTOS ticks (TickType_t)
Receiving
Once the data is received by the UART and saved in the Rx FIFO buffer, it needs to be retrieved using the function uart_read_bytes(). Before reading data, you can check the number of bytes available in the Rx FIFO buffer by calling uart_get_buffered_data_len(). An example of using these functions is given below.
// Read data from UART.
const uart_port_t uart_num = UART_NUM_1;
uint8_t data[128];
int length = 0;
ESP_ERROR_CHECK(uart_get_buffered_data_len(uart_num, (size_t*)&length));
length = uart_read_bytes(uart_num, data, length, 100);
If the data in the Rx FIFO buffer is no longer needed, you can clear the buffer by calling uart_flush().
Software Flow Control
If the hardware flow control is disabled, you can manually set the RTS and DTR signal levels by using the functions uart_set_rts() and uart_set_dtr() respectively.
Communication Mode Selection
The UART controller supports a number of communication modes. A mode can be selected using the function uart_set_mode(). Once a specific mode is selected, the UART driver will handle the behavior of a connected UART device accordingly. As an example, it can control the RS485 driver chip using the RTS line to allow half-duplex RS485 communication.
// Setup UART in rs485 half duplex mode
ESP_ERROR_CHECK(uart_set_mode(uart_num, UART_MODE_RS485_HALF_DUPLEX));
Using Interrupts
There are many interrupts that can be generated following specific UART states or detected errors. The full list of available interrupts is provided in ESP32-C3 Technical Reference Manual > UART Controller (UART) > UART Interrupts and UHCI Interrupts [PDF]. You can enable or disable specific interrupts by calling uart_enable_intr_mask() or uart_disable_intr_mask() respectively. The mask of all interrupts is available as UART_INTR_MASK.
By default, the uart_driver_install() function installs the driver’s internal interrupt handler to manage the Tx and Rx ring buffers and provides high-level API functions like events (see below). It is also possible to register a lower level interrupt handler instead using uart_isr_register(), and to free it again using uart_isr_free(). Some UART driver functions which use the Tx and Rx ring buffers, events, etc. will not automatically work in this case - it is necessary to handle the interrupts directly in the ISR. Inside the custom handler implementation, clear the interrupt status bits using uart_clear_intr_status().
The API provides a convenient way to handle specific interrupts discussed in this document by wrapping them into dedicated functions:
Event detection: There are several events defined in
uart_event_type_tthat may be reported to a user application using the FreeRTOS queue functionality. You can enable this functionality when callinguart_driver_install()described in Driver Installation. An example of using Event detection can be found in peripherals/uart/uart_events.FIFO space threshold or transmission timeout reached: The Tx and Rx FIFO buffers can trigger an interrupt when they are filled with a specific number of characters, or on a timeout of sending or receiving data. To use these interrupts, do the following:
Configure respective threshold values of the buffer length and timeout by entering them in the structure
uart_intr_config_tand callinguart_intr_config()Enable the interrupts using the functions
uart_enable_tx_intr()anduart_enable_rx_intr()Disable these interrupts using the corresponding functions
uart_disable_tx_intr()oruart_disable_rx_intr()
Pattern detection: An interrupt triggered on detecting a ‘pattern’ of the same character being received/sent repeatedly for a number of times. This functionality is demonstrated in the example peripherals/uart/uart_events. It can be used, e.g., to detect a command string followed by a specific number of identical characters (the ‘pattern’) added at the end of the command string. The following functions are available:
Configure and enable this interrupt using
uart_enable_pattern_det_intr()Disable the interrupt using
uart_disable_pattern_det_intr()
Macros
The API also defines several macros. For example, UART_FIFO_LEN defines the length of hardware FIFO buffers; UART_BITRATE_MAX gives the maximum baud rate supported by the UART controllers, etc.
Deleting a Driver
If the communication established with uart_driver_install() is no longer required, the driver can be removed to free allocated resources by calling uart_driver_delete().
Overview of RS485 specific communication options
Note
The following section will use [UART_REGISTER_NAME].[UART_FIELD_BIT] to refer to UART register fields/bits. For more information on a specific option bit, see ESP32-C3 Technical Reference Manual > UART Controller (UART) > Register Summary [PDF]. Use the register name to navigate to the register description and then find the field/bit.
UART_RS485_CONF_REG.UART_RS485_EN: setting this bit enables RS485 communication mode support.UART_RS485_CONF_REG.UART_RS485TX_RX_EN: if this bit is set, the transmitter’s output signal loops back to the receiver’s input signal.UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN: if this bit is set, the transmitter will still be sending data if the receiver is busy (remove collisions automatically by hardware).
The ESP32-C3’s RS485 UART hardware can detect signal collisions during transmission of a datagram and generate the interrupt UART_RS485_CLASH_INT if this interrupt is enabled. The term collision means that a transmitted datagram is not equal to the one received on the other end. Data collisions are usually associated with the presence of other active devices on the bus or might occur due to bus errors.
The collision detection feature allows handling collisions when their interrupts are activated and triggered. The interrupts UART_RS485_FRM_ERR_INT and UART_RS485_PARITY_ERR_INT can be used with the collision detection feature to control frame errors and parity bit errors accordingly in RS485 mode. This functionality is supported in the UART driver and can be used by selecting the UART_MODE_RS485_APP_CTRL mode (see the function uart_set_mode()).
The collision detection feature can work with circuit A and circuit C (see Section Interface Connection Options). In the case of using circuit A or B, the RTS pin connected to the DE pin of the bus driver should be controlled by the user application. Use the function uart_get_collision_flag() to check if the collision detection flag has been raised.
The ESP32-C3 UART controllers themselves do not support half-duplex communication as they cannot provide automatic control of the RTS pin connected to the ~RE/DE input of RS485 bus driver. However, half-duplex communication can be achieved via software control of the RTS pin by the UART driver. This can be enabled by selecting the UART_MODE_RS485_HALF_DUPLEX mode when calling uart_set_mode().
Once the host starts writing data to the Tx FIFO buffer, the UART driver automatically asserts the RTS pin (logic 1); once the last bit of the data has been transmitted, the driver de-asserts the RTS pin (logic 0). To use this mode, the software would have to disable the hardware flow control function. This mode works with all the used circuits shown below.
Interface Connection Options
This section provides example schematics to demonstrate the basic aspects of ESP32-C3’s RS485 interface connection.
Note
The schematics below do not necessarily contain all required elements.
The analog devices ADM483 & ADM2483 are examples of common RS485 transceivers and can be replaced with other similar transceivers.
Circuit A: Collision Detection Circuit
VCC ---------------+
|
+-------x-------+
RXD <------| R |
| B|----------<> B
TXD ------>| D ADM483 |
ESP | | RS485 bus side
RTS ------>| DE |
| A|----------<> A
+----| /RE |
| +-------x-------+
| |
GND GND
This circuit is preferable because it allows for collision detection and is quite simple at the same time. The receiver in the line driver is constantly enabled, which allows the UART to monitor the RS485 bus. Echo suppression is performed by the UART peripheral when the bit UART_RS485_CONF_REG.UART_RS485TX_RX_EN is enabled.
Circuit B: Manual Switching Transmitter/Receiver Without Collision Detection
VCC ---------------+
|
+-------x-------+
RXD <------| R |
| B|-----------<> B
TXD ------>| D ADM483 |
ESP | | RS485 bus side
RTS --+--->| DE |
| | A|-----------<> A
+----| /RE |
+-------x-------+
|
GND
This circuit does not allow for collision detection. It suppresses the null bytes that the hardware receives when the bit UART_RS485_CONF_REG.UART_RS485TX_RX_EN is set. The bit UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN is not applicable in this case.
Circuit C: Auto Switching Transmitter/Receiver
VCC1 <-------------------+-----------+ +-------------------+----> VCC2
10K ____ | | | |
+---|____|--+ +---x-----------x---+ 10K ____ |
| | | +---|____|--+
RX <----------+-------------------| RXD | |
10K ____ | A|---+---------------<> A (+)
+-------|____|------| PV ADM2483 | | ____ 120
| ____ | | +---|____|---+ RS485 bus side
VCC1 <--+--|____|--+------->| DE | |
10K | | B|---+------------+--<> B (-)
---+ +-->| /RE | | ____
10K | | | | +---|____|---+
____ | /-C +---| TXD | 10K |
TX >---|____|--+_B_|/ NPN | | | |
|\ | +---x-----------x---+ |
| \-E | | | |
| | | | |
GND1 GND1 GND1 GND2 GND2
This galvanically isolated circuit does not require RTS pin control by a software application or driver because it controls the transceiver direction automatically. However, it requires suppressing null bytes during transmission by setting UART_RS485_CONF_REG.UART_RS485RXBY_TX_EN to 1 and UART_RS485_CONF_REG.UART_RS485TX_RX_EN to 0. This setup can work in any RS485 UART mode or even in UART_MODE_UART.
Application Examples
The table below describes the code examples available in the directory peripherals/uart/.
Code Example |
Description |
|---|---|
Configuring UART settings, installing the UART driver, and reading/writing over the UART1 interface. |
|
Reporting various communication events, using pattern detection interrupts. |
|
Transmitting and receiving data in two separate FreeRTOS tasks over the same UART. |
|
Using synchronous I/O multiplexing for UART file descriptors. |
|
Setting up UART driver to communicate over RS485 interface in half-duplex mode. This example is similar to peripherals/uart/uart_echo but allows communication through an RS485 interface chip connected to ESP32-C3 pins. |
|
Obtaining GPS information by parsing NMEA0183 statements received from GPS via the UART peripheral. |
API Reference
Header File
Functions
-
esp_err_t uart_driver_install(uart_port_t uart_num, int rx_buffer_size, int tx_buffer_size, int queue_size, QueueHandle_t *uart_queue, int intr_alloc_flags)
Install UART driver and set the UART to the default configuration.
UART ISR handler will be attached to the same CPU core that this function is running on.
Note
Rx_buffer_size should be greater than UART_FIFO_LEN. Tx_buffer_size should be either zero or greater than UART_FIFO_LEN.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
rx_buffer_size – UART RX ring buffer size.
tx_buffer_size – UART TX ring buffer size. If set to zero, driver will not use TX buffer, TX function will block task until all data have been sent out.
queue_size – UART event queue size/depth.
uart_queue – UART event queue handle (out param). On success, a new queue handle is written here to provide access to UART events. If set to NULL, driver will not use an event queue.
intr_alloc_flags – Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info. Do not set ESP_INTR_FLAG_IRAM here (the driver’s ISR handler is not located in IRAM)
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_driver_delete(uart_port_t uart_num)
Uninstall UART driver.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
bool uart_is_driver_installed(uart_port_t uart_num)
Checks whether the driver is installed or not.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
true driver is installed
false driver is not installed
-
esp_err_t uart_set_word_length(uart_port_t uart_num, uart_word_length_t data_bit)
Set UART data bits.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
data_bit – UART data bits
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_get_word_length(uart_port_t uart_num, uart_word_length_t *data_bit)
Get the UART data bit configuration.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
data_bit – Pointer to accept value of UART data bits.
- Returns
ESP_FAIL Parameter error
ESP_OK Success, result will be put in (*data_bit)
-
esp_err_t uart_set_stop_bits(uart_port_t uart_num, uart_stop_bits_t stop_bits)
Set UART stop bits.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
stop_bits – UART stop bits
- Returns
ESP_OK Success
ESP_FAIL Fail
-
esp_err_t uart_get_stop_bits(uart_port_t uart_num, uart_stop_bits_t *stop_bits)
Get the UART stop bit configuration.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
stop_bits – Pointer to accept value of UART stop bits.
- Returns
ESP_FAIL Parameter error
ESP_OK Success, result will be put in (*stop_bit)
-
esp_err_t uart_set_parity(uart_port_t uart_num, uart_parity_t parity_mode)
Set UART parity mode.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
parity_mode – the enum of uart parity configuration
- Returns
ESP_FAIL Parameter error
ESP_OK Success
-
esp_err_t uart_get_parity(uart_port_t uart_num, uart_parity_t *parity_mode)
Get the UART parity mode configuration.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
parity_mode – Pointer to accept value of UART parity mode.
- Returns
ESP_FAIL Parameter error
ESP_OK Success, result will be put in (*parity_mode)
-
esp_err_t uart_set_baudrate(uart_port_t uart_num, uint32_t baudrate)
Set UART baud rate.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
baudrate – UART baud rate.
- Returns
ESP_FAIL Parameter error
ESP_OK Success
-
esp_err_t uart_get_baudrate(uart_port_t uart_num, uint32_t *baudrate)
Get the UART baud rate configuration.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
baudrate – Pointer to accept value of UART baud rate
- Returns
ESP_FAIL Parameter error
ESP_OK Success, result will be put in (*baudrate)
-
esp_err_t uart_set_line_inverse(uart_port_t uart_num, uint32_t inverse_mask)
Set UART line inverse mode.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
inverse_mask – Choose the wires that need to be inverted. Using the ORred mask of
uart_signal_inv_t
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_set_hw_flow_ctrl(uart_port_t uart_num, uart_hw_flowcontrol_t flow_ctrl, uint8_t rx_thresh)
Set hardware flow control.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
flow_ctrl – Hardware flow control mode
rx_thresh – Threshold of Hardware RX flow control (0 ~ UART_FIFO_LEN). Only when UART_HW_FLOWCTRL_RTS is set, will the rx_thresh value be set.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_set_sw_flow_ctrl(uart_port_t uart_num, bool enable, uint8_t rx_thresh_xon, uint8_t rx_thresh_xoff)
Set software flow control.
- Parameters
uart_num – UART_NUM_0, UART_NUM_1 or UART_NUM_2
enable – switch on or off
rx_thresh_xon – low water mark
rx_thresh_xoff – high water mark
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_get_hw_flow_ctrl(uart_port_t uart_num, uart_hw_flowcontrol_t *flow_ctrl)
Get the UART hardware flow control configuration.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
flow_ctrl – Option for different flow control mode.
- Returns
ESP_FAIL Parameter error
ESP_OK Success, result will be put in (*flow_ctrl)
-
esp_err_t uart_clear_intr_status(uart_port_t uart_num, uint32_t clr_mask)
Clear UART interrupt status.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
clr_mask – Bit mask of the interrupt status to be cleared.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_enable_intr_mask(uart_port_t uart_num, uint32_t enable_mask)
Set UART interrupt enable.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
enable_mask – Bit mask of the enable bits.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_disable_intr_mask(uart_port_t uart_num, uint32_t disable_mask)
Clear UART interrupt enable bits.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
disable_mask – Bit mask of the disable bits.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_enable_rx_intr(uart_port_t uart_num)
Enable UART RX interrupt (RX_FULL & RX_TIMEOUT INTERRUPT)
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_disable_rx_intr(uart_port_t uart_num)
Disable UART RX interrupt (RX_FULL & RX_TIMEOUT INTERRUPT)
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_disable_tx_intr(uart_port_t uart_num)
Disable UART TX interrupt (TXFIFO_EMPTY INTERRUPT)
- Parameters
uart_num – UART port number
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_enable_tx_intr(uart_port_t uart_num, int enable, int thresh)
Enable UART TX interrupt (TXFIFO_EMPTY INTERRUPT)
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
enable – 1: enable; 0: disable
thresh – Threshold of TX interrupt, 0 ~ UART_FIFO_LEN
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_isr_register(uart_port_t uart_num, void (*fn)(void*), void *arg, int intr_alloc_flags, uart_isr_handle_t *handle)
Register UART interrupt handler (ISR).
Note
UART ISR handler will be attached to the same CPU core that this function is running on.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
fn – Interrupt handler function.
arg – parameter for handler function
intr_alloc_flags – Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info.
handle – Pointer to return handle. If non-NULL, a handle for the interrupt will be returned here.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_isr_free(uart_port_t uart_num)
Free UART interrupt handler registered by uart_isr_register. Must be called on the same core as uart_isr_register was called.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_set_pin(uart_port_t uart_num, int tx_io_num, int rx_io_num, int rts_io_num, int cts_io_num)
Assign signals of a UART peripheral to GPIO pins.
Note
If the GPIO number configured for a UART signal matches one of the IOMUX signals for that GPIO, the signal will be connected directly via the IOMUX. Otherwise the GPIO and signal will be connected via the GPIO Matrix. For example, if on an ESP32 the call
uart_set_pin(0, 1, 3, -1, -1)is performed, as GPIO1 is UART0’s default TX pin and GPIO3 is UART0’s default RX pin, both will be connected to respectively U0TXD and U0RXD through the IOMUX, totally bypassing the GPIO matrix. The check is performed on a per-pin basis. Thus, it is possible to have RX pin binded to a GPIO through the GPIO matrix, whereas TX is binded to its GPIO through the IOMUX.Note
Internal signal can be output to multiple GPIO pads. Only one GPIO pad can connect with input signal.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
tx_io_num – UART TX pin GPIO number.
rx_io_num – UART RX pin GPIO number.
rts_io_num – UART RTS pin GPIO number.
cts_io_num – UART CTS pin GPIO number.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_set_rts(uart_port_t uart_num, int level)
Manually set the UART RTS pin level.
Note
UART must be configured with hardware flow control disabled.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
level – 1: RTS output low (active); 0: RTS output high (block)
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_set_dtr(uart_port_t uart_num, int level)
Manually set the UART DTR pin level.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
level – 1: DTR output low; 0: DTR output high
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_set_tx_idle_num(uart_port_t uart_num, uint16_t idle_num)
Set UART idle interval after tx FIFO is empty.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
idle_num – idle interval after tx FIFO is empty(unit: the time it takes to send one bit under current baudrate)
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_param_config(uart_port_t uart_num, const uart_config_t *uart_config)
Set UART configuration parameters.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
uart_config – UART parameter settings
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_intr_config(uart_port_t uart_num, const uart_intr_config_t *intr_conf)
Configure UART interrupts.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
intr_conf – UART interrupt settings
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_wait_tx_done(uart_port_t uart_num, TickType_t ticks_to_wait)
Wait until UART TX FIFO is empty.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
ticks_to_wait – Timeout, count in RTOS ticks
- Returns
ESP_OK Success
ESP_FAIL Parameter error
ESP_ERR_TIMEOUT Timeout
-
int uart_tx_chars(uart_port_t uart_num, const char *buffer, uint32_t len)
Send data to the UART port from a given buffer and length.
This function will not wait for enough space in TX FIFO. It will just fill the available TX FIFO and return when the FIFO is full.
Note
This function should only be used when UART TX buffer is not enabled.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
buffer – data buffer address
len – data length to send
- Returns
(-1) Parameter error
OTHERS (>=0) The number of bytes pushed to the TX FIFO
-
int uart_write_bytes(uart_port_t uart_num, const void *src, size_t size)
Send data to the UART port from a given buffer and length,.
If the UART driver’s parameter ‘tx_buffer_size’ is set to zero: This function will not return until all the data have been sent out, or at least pushed into TX FIFO.
Otherwise, if the ‘tx_buffer_size’ > 0, this function will return after copying all the data to tx ring buffer, UART ISR will then move data from the ring buffer to TX FIFO gradually.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
src – data buffer address
size – data length to send
- Returns
(-1) Parameter error
OTHERS (>=0) The number of bytes pushed to the TX FIFO
-
int uart_write_bytes_with_break(uart_port_t uart_num, const void *src, size_t size, int brk_len)
Send data to the UART port from a given buffer and length,.
If the UART driver’s parameter ‘tx_buffer_size’ is set to zero: This function will not return until all the data and the break signal have been sent out. After all data is sent out, send a break signal.
Otherwise, if the ‘tx_buffer_size’ > 0, this function will return after copying all the data to tx ring buffer, UART ISR will then move data from the ring buffer to TX FIFO gradually. After all data sent out, send a break signal.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
src – data buffer address
size – data length to send
brk_len – break signal duration(unit: the time it takes to send one bit at current baudrate)
- Returns
(-1) Parameter error
OTHERS (>=0) The number of bytes pushed to the TX FIFO
-
int uart_read_bytes(uart_port_t uart_num, void *buf, uint32_t length, TickType_t ticks_to_wait)
UART read bytes from UART buffer.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
buf – pointer to the buffer.
length – data length
ticks_to_wait – sTimeout, count in RTOS ticks
- Returns
(-1) Error
OTHERS (>=0) The number of bytes read from UART FIFO
-
esp_err_t uart_flush(uart_port_t uart_num)
Alias of uart_flush_input. UART ring buffer flush. This will discard all data in the UART RX buffer.
Note
Instead of waiting the data sent out, this function will clear UART rx buffer. In order to send all the data in tx FIFO, we can use uart_wait_tx_done function.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_flush_input(uart_port_t uart_num)
Clear input buffer, discard all the data is in the ring-buffer.
Note
In order to send all the data in tx FIFO, we can use uart_wait_tx_done function.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_get_buffered_data_len(uart_port_t uart_num, size_t *size)
UART get RX ring buffer cached data length.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
size – Pointer of size_t to accept cached data length
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_get_tx_buffer_free_size(uart_port_t uart_num, size_t *size)
UART get TX ring buffer free space size.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
size – Pointer of size_t to accept the free space size
- Returns
ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
-
esp_err_t uart_disable_pattern_det_intr(uart_port_t uart_num)
UART disable pattern detect function. Designed for applications like ‘AT commands’. When the hardware detects a series of one same character, the interrupt will be triggered.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
esp_err_t uart_enable_pattern_det_baud_intr(uart_port_t uart_num, char pattern_chr, uint8_t chr_num, int chr_tout, int post_idle, int pre_idle)
UART enable pattern detect function. Designed for applications like ‘AT commands’. When the hardware detect a series of one same character, the interrupt will be triggered.
- Parameters
uart_num – UART port number.
pattern_chr – character of the pattern.
chr_num – number of the character, 8bit value.
chr_tout – timeout of the interval between each pattern characters, 16bit value, unit is the baud-rate cycle you configured. When the duration is more than this value, it will not take this data as at_cmd char.
post_idle – idle time after the last pattern character, 16bit value, unit is the baud-rate cycle you configured. When the duration is less than this value, it will not take the previous data as the last at_cmd char
pre_idle – idle time before the first pattern character, 16bit value, unit is the baud-rate cycle you configured. When the duration is less than this value, it will not take this data as the first at_cmd char.
- Returns
ESP_OK Success
ESP_FAIL Parameter error
-
int uart_pattern_pop_pos(uart_port_t uart_num)
Return the nearest detected pattern position in buffer. The positions of the detected pattern are saved in a queue, this function will dequeue the first pattern position and move the pointer to next pattern position.
The following APIs will modify the pattern position info: uart_flush_input, uart_read_bytes, uart_driver_delete, uart_pop_pattern_pos It is the application’s responsibility to ensure atomic access to the pattern queue and the rx data buffer when using pattern detect feature.
Note
If the RX buffer is full and flow control is not enabled, the detected pattern may not be found in the rx buffer due to overflow.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
(-1) No pattern found for current index or parameter error
others the pattern position in rx buffer.
-
int uart_pattern_get_pos(uart_port_t uart_num)
Return the nearest detected pattern position in buffer. The positions of the detected pattern are saved in a queue, This function do nothing to the queue.
The following APIs will modify the pattern position info: uart_flush_input, uart_read_bytes, uart_driver_delete, uart_pop_pattern_pos It is the application’s responsibility to ensure atomic access to the pattern queue and the rx data buffer when using pattern detect feature.
Note
If the RX buffer is full and flow control is not enabled, the detected pattern may not be found in the rx buffer due to overflow.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
- Returns
(-1) No pattern found for current index or parameter error
others the pattern position in rx buffer.
-
esp_err_t uart_pattern_queue_reset(uart_port_t uart_num, int queue_length)
Allocate a new memory with the given length to save record the detected pattern position in rx buffer.
- Parameters
uart_num – UART port number, the max port number is (UART_NUM_MAX -1).
queue_length – Max queue length for the detected pattern. If the queue length is not large enough, some pattern positions might be lost. Set this value to the maximum number of patterns that could be saved in data buffer at the same time.
- Returns
ESP_ERR_NO_MEM No enough memory
ESP_ERR_INVALID_STATE Driver not installed
ESP_FAIL Parameter error
ESP_OK Success
-
esp_err_t uart_set_mode(uart_port_t uart_num, uart_mode_t mode)
UART set communication mode.
Note
This function must be executed after uart_driver_install(), when the driver object is initialized.
- Parameters
uart_num – Uart number to configure, the max port number is (UART_NUM_MAX -1).
mode – UART UART mode to set
- Returns
ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
-
esp_err_t uart_set_rx_full_threshold(uart_port_t uart_num, int threshold)
Set uart threshold value for RX fifo full.
Note
If application is using higher baudrate and it is observed that bytes in hardware RX fifo are overwritten then this threshold can be reduced
- Parameters
uart_num – UART_NUM_0, UART_NUM_1 or UART_NUM_2
threshold – Threshold value above which RX fifo full interrupt is generated
- Returns
ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_INVALID_STATE Driver is not installed
-
esp_err_t uart_set_tx_empty_threshold(uart_port_t uart_num, int threshold)
Set uart threshold values for TX fifo empty.
- Parameters
uart_num – UART_NUM_0, UART_NUM_1 or UART_NUM_2
threshold – Threshold value below which TX fifo empty interrupt is generated
- Returns
ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_INVALID_STATE Driver is not installed
-
esp_err_t uart_set_rx_timeout(uart_port_t uart_num, const uint8_t tout_thresh)
UART set threshold timeout for TOUT feature.
- Parameters
uart_num – Uart number to configure, the max port number is (UART_NUM_MAX -1).
tout_thresh – This parameter defines timeout threshold in uart symbol periods. The maximum value of threshold is 126. tout_thresh = 1, defines TOUT interrupt timeout equal to transmission time of one symbol (~11 bit) on current baudrate. If the time is expired the UART_RXFIFO_TOUT_INT interrupt is triggered. If tout_thresh == 0, the TOUT feature is disabled.
- Returns
ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
ESP_ERR_INVALID_STATE Driver is not installed
-
esp_err_t uart_get_collision_flag(uart_port_t uart_num, bool *collision_flag)
Returns collision detection flag for RS485 mode Function returns the collision detection flag into variable pointed by collision_flag. *collision_flag = true, if collision detected else it is equal to false. This function should be executed when actual transmission is completed (after uart_write_bytes()).
- Parameters
uart_num – Uart number to configure the max port number is (UART_NUM_MAX -1).
collision_flag – Pointer to variable of type bool to return collision flag.
- Returns
ESP_OK Success
ESP_ERR_INVALID_ARG Parameter error
-
esp_err_t uart_set_wakeup_threshold(uart_port_t uart_num, int wakeup_threshold)
Set the number of RX pin signal edges for light sleep wakeup.
UART can be used to wake up the system from light sleep. This feature works by counting the number of positive edges on RX pin and comparing the count to the threshold. When the count exceeds the threshold, system is woken up from light sleep. This function allows setting the threshold value.
Stop bit and parity bits (if enabled) also contribute to the number of edges. For example, letter ‘a’ with ASCII code 97 is encoded as 0100001101 on the wire (with 8n1 configuration), start and stop bits included. This sequence has 3 positive edges (transitions from 0 to 1). Therefore, to wake up the system when ‘a’ is sent, set wakeup_threshold=3.
The character that triggers wakeup is not received by UART (i.e. it can not be obtained from UART FIFO). Depending on the baud rate, a few characters after that will also not be received. Note that when the chip enters and exits light sleep mode, APB frequency will be changing. To make sure that UART has correct baud rate all the time, select REF_TICK as UART clock source, by setting use_ref_tick field in uart_config_t to true.
Note
in ESP32, the wakeup signal can only be input via IO_MUX (i.e. GPIO3 should be configured as function_1 to wake up UART0, GPIO9 should be configured as function_5 to wake up UART1), UART2 does not support light sleep wakeup feature.
- Parameters
uart_num – UART number, the max port number is (UART_NUM_MAX -1).
wakeup_threshold – number of RX edges for light sleep wakeup, value is 3 .. 0x3ff.
- Returns
ESP_OK on success
ESP_ERR_INVALID_ARG if uart_num is incorrect or wakeup_threshold is outside of [3, 0x3ff] range.
-
esp_err_t uart_get_wakeup_threshold(uart_port_t uart_num, int *out_wakeup_threshold)
Get the number of RX pin signal edges for light sleep wakeup.
See description of uart_set_wakeup_threshold for the explanation of UART wakeup feature.
- Parameters
uart_num – UART number, the max port number is (UART_NUM_MAX -1).
out_wakeup_threshold – [out] output, set to the current value of wakeup threshold for the given UART.
- Returns
ESP_OK on success
ESP_ERR_INVALID_ARG if out_wakeup_threshold is NULL
-
esp_err_t uart_wait_tx_idle_polling(uart_port_t uart_num)
Wait until UART tx memory empty and the last char send ok (polling mode).
- Returns
ESP_OK on success
ESP_ERR_INVALID_ARG Parameter error
ESP_FAIL Driver not installed
- Parameters
uart_num – UART number
-
esp_err_t uart_set_loop_back(uart_port_t uart_num, bool loop_back_en)
Configure TX signal loop back to RX module, just for the test usage.
- Returns
ESP_OK on success
ESP_ERR_INVALID_ARG Parameter error
ESP_FAIL Driver not installed
- Parameters
uart_num – UART number
loop_back_en – Set ture to enable the loop back function, else set it false.
-
void uart_set_always_rx_timeout(uart_port_t uart_num, bool always_rx_timeout_en)
Configure behavior of UART RX timeout interrupt.
When always_rx_timeout is true, timeout interrupt is triggered even if FIFO is full. This function can cause extra timeout interrupts triggered only to send the timeout event. Call this function only if you want to ensure timeout interrupt will always happen after a byte stream.
- Parameters
uart_num – UART number
always_rx_timeout_en – Set to false enable the default behavior of timeout interrupt, set it to true to always trigger timeout interrupt.
Structures
-
struct uart_intr_config_t
UART interrupt configuration parameters for uart_intr_config function.
Public Members
-
uint32_t intr_enable_mask
UART interrupt enable mask, choose from UART_XXXX_INT_ENA_M under UART_INT_ENA_REG(i), connect with bit-or operator
-
uint8_t rx_timeout_thresh
UART timeout interrupt threshold (unit: time of sending one byte)
-
uint8_t txfifo_empty_intr_thresh
UART TX empty interrupt threshold.
-
uint8_t rxfifo_full_thresh
UART RX full interrupt threshold.
-
uint32_t intr_enable_mask
-
struct uart_event_t
Event structure used in UART event queue.
Public Members
-
uart_event_type_t type
UART event type
-
size_t size
UART data size for UART_DATA event
-
bool timeout_flag
UART data read timeout flag for UART_DATA event (no new data received during configured RX TOUT) If the event is caused by FIFO-full interrupt, then there will be no event with the timeout flag before the next byte coming.
-
uart_event_type_t type
Macros
-
UART_NUM_0
UART port 0
-
UART_NUM_1
UART port 1
-
UART_NUM_MAX
UART port max
-
UART_PIN_NO_CHANGE
-
UART_FIFO_LEN
Length of the UART HW FIFO.
-
UART_BITRATE_MAX
Maximum configurable bitrate.
Type Definitions
-
typedef intr_handle_t uart_isr_handle_t
Enumerations
-
enum uart_event_type_t
UART event types used in the ring buffer.
Values:
-
enumerator UART_DATA
UART data event
-
enumerator UART_BREAK
UART break event
-
enumerator UART_BUFFER_FULL
UART RX buffer full event
-
enumerator UART_FIFO_OVF
UART FIFO overflow event
-
enumerator UART_FRAME_ERR
UART RX frame error event
-
enumerator UART_PARITY_ERR
UART RX parity event
-
enumerator UART_DATA_BREAK
UART TX data and break event
-
enumerator UART_PATTERN_DET
UART pattern detected
-
enumerator UART_WAKEUP
UART wakeup event
-
enumerator UART_EVENT_MAX
UART event max index
-
enumerator UART_DATA
Header File
Structures
-
struct uart_at_cmd_t
UART AT cmd char configuration parameters Note that this function may different on different chip. Please refer to the TRM at confirguration.
Public Members
-
uint8_t cmd_char
UART AT cmd char
-
uint8_t char_num
AT cmd char repeat number
-
uint32_t gap_tout
gap time(in baud-rate) between AT cmd char
-
uint32_t pre_idle
the idle time(in baud-rate) between the non AT char and first AT char
-
uint32_t post_idle
the idle time(in baud-rate) between the last AT char and the none AT char
-
uint8_t cmd_char
-
struct uart_sw_flowctrl_t
UART software flow control configuration parameters.
Public Members
-
uint8_t xon_char
Xon flow control char
-
uint8_t xoff_char
Xoff flow control char
-
uint8_t xon_thrd
If the software flow control is enabled and the data amount in rxfifo is less than xon_thrd, an xon_char will be sent
-
uint8_t xoff_thrd
If the software flow control is enabled and the data amount in rxfifo is more than xoff_thrd, an xoff_char will be sent
-
uint8_t xon_char
-
struct uart_config_t
UART configuration parameters for uart_param_config function.
Public Members
-
int baud_rate
UART baud rate
-
uart_word_length_t data_bits
UART byte size
-
uart_parity_t parity
UART parity mode
-
uart_stop_bits_t stop_bits
UART stop bits
-
uart_hw_flowcontrol_t flow_ctrl
UART HW flow control mode (cts/rts)
-
uint8_t rx_flow_ctrl_thresh
UART HW RTS threshold
-
uart_sclk_t source_clk
UART source clock selection
-
bool use_ref_tick
Deprecated method to select ref tick clock source, set source_clk field instead
-
int baud_rate
Enumerations
-
enum uart_mode_t
UART mode selection.
Values:
-
enumerator UART_MODE_UART
mode: regular UART mode
-
enumerator UART_MODE_RS485_HALF_DUPLEX
mode: half duplex RS485 UART mode control by RTS pin
-
enumerator UART_MODE_IRDA
mode: IRDA UART mode
-
enumerator UART_MODE_RS485_COLLISION_DETECT
mode: RS485 collision detection UART mode (used for test purposes)
-
enumerator UART_MODE_RS485_APP_CTRL
mode: application control RS485 UART mode (used for test purposes)
-
enumerator UART_MODE_UART
-
enum uart_word_length_t
UART word length constants.
Values:
-
enumerator UART_DATA_5_BITS
word length: 5bits
-
enumerator UART_DATA_6_BITS
word length: 6bits
-
enumerator UART_DATA_7_BITS
word length: 7bits
-
enumerator UART_DATA_8_BITS
word length: 8bits
-
enumerator UART_DATA_BITS_MAX
-
enumerator UART_DATA_5_BITS
-
enum uart_stop_bits_t
UART stop bits number.
Values:
-
enumerator UART_STOP_BITS_1
stop bit: 1bit
-
enumerator UART_STOP_BITS_1_5
stop bit: 1.5bits
-
enumerator UART_STOP_BITS_2
stop bit: 2bits
-
enumerator UART_STOP_BITS_MAX
-
enumerator UART_STOP_BITS_1
-
enum uart_parity_t
UART parity constants.
Values:
-
enumerator UART_PARITY_DISABLE
Disable UART parity
-
enumerator UART_PARITY_EVEN
Enable UART even parity
-
enumerator UART_PARITY_ODD
Enable UART odd parity
-
enumerator UART_PARITY_DISABLE
-
enum uart_hw_flowcontrol_t
UART hardware flow control modes.
Values:
-
enumerator UART_HW_FLOWCTRL_DISABLE
disable hardware flow control
-
enumerator UART_HW_FLOWCTRL_RTS
enable RX hardware flow control (rts)
-
enumerator UART_HW_FLOWCTRL_CTS
enable TX hardware flow control (cts)
-
enumerator UART_HW_FLOWCTRL_CTS_RTS
enable hardware flow control
-
enumerator UART_HW_FLOWCTRL_MAX
-
enumerator UART_HW_FLOWCTRL_DISABLE
-
enum uart_signal_inv_t
UART signal bit map.
Values:
-
enumerator UART_SIGNAL_INV_DISABLE
Disable UART signal inverse
-
enumerator UART_SIGNAL_IRDA_TX_INV
inverse the UART irda_tx signal
-
enumerator UART_SIGNAL_IRDA_RX_INV
inverse the UART irda_rx signal
-
enumerator UART_SIGNAL_RXD_INV
inverse the UART rxd signal
-
enumerator UART_SIGNAL_CTS_INV
inverse the UART cts signal
-
enumerator UART_SIGNAL_DSR_INV
inverse the UART dsr signal
-
enumerator UART_SIGNAL_TXD_INV
inverse the UART txd signal
-
enumerator UART_SIGNAL_RTS_INV
inverse the UART rts signal
-
enumerator UART_SIGNAL_DTR_INV
inverse the UART dtr signal
-
enumerator UART_SIGNAL_INV_DISABLE
GPIO Lookup Macros
The UART peripherals have dedicated IO_MUX pins to which they are connected directly. However, signals can also be routed to other pins using the less direct GPIO matrix. To use direct routes, you need to know which pin is a dedicated IO_MUX pin for a UART channel. GPIO Lookup Macros simplify the process of finding and assigning IO_MUX pins. You choose a macro based on either the IO_MUX pin number, or a required UART channel name, and the macro will return the matching counterpart for you. See some examples below.
Note
These macros are useful if you need very high UART baud rates (over 40 MHz), which means you will have to use IO_MUX pins only. In other cases, these macros can be ignored, and you can use the GPIO Matrix as it allows you to configure any GPIO pin for any UART function.
UART_NUM_2_TXD_DIRECT_GPIO_NUMreturns the IO_MUX pin number of UART channel 2 TXD pin (pin 17)UART_GPIO19_DIRECT_CHANNELreturns the UART number of GPIO 19 when connected to the UART peripheral via IO_MUX (this is UART_NUM_0)UART_CTS_GPIO19_DIRECT_CHANNELreturns the UART number of GPIO 19 when used as the UART CTS pin via IO_MUX (this is UART_NUM_0). Similar to the above macro but specifies the pin function which is also part of the IO_MUX assignment.