So hello guys, welcome back to NXP Semiconductors S32K144 MCU Tutorial series. In the last blog we had started with S32K144 MCU GPIO Peripheral. In this blog we are going to explore the UART Peripheral. Going to Start with UART peripheral. Objective would be to get.
- familiarity with UART peripheral for S32K144 MCU.
- Would be understanding UART peripheral from Hardware point of view in S32K144 MCU.
- Going to understand then how to use UART peripheral via S32K SDK/uart driver.
- Would also be demonstrating the uart_echo_pall sketch.
So read along the blog and do tell me its reviews!
Table of Contents
UART Peripheral Theory
UART is a serial communication protocol which is used to interface external sensor & IoT modules to the Host MCU. IoT modules like: GSM Module, GPS Module, BLE Modules, WiFi Modules are connected to Host MCU via UART protocol. Thus, understanding of UART communication protocol and its driver implementation, plays a crucial role.
To know about UART peripheral in theory, viewers can refer to this blog.
LPUART Peripheral in S32K144 MCU
In S32K144 MCU, UART can be used via 2 peripherals: LPUART & FlexIO.
LPUART is referred as Low Power Universal Asynchronous Receiver/Transmitter. LPUART is onchip peripheral only to do UART communication protocol. UART is a serial communication protocol which is done via UART peripheral in the Microcontrollers.
Also, in S32K144, there is FlexIO peripheral through which on-board serial communication protocols like UART, I2C & SPI can be emulated. So, through FlexIO peripheral, also UART peripheral can be implemented. To know about FlexIO peripheral in S32K144, refer to this blog.
Features of UART via LPUART peripheral in S32K144 MCU:
- LPUART peripheral of S32K144 supports full duplex mode and has NRZ data encoding (That is Logic 1 bit represents High value and Logic 0 bit represents Low value).
- It has programmable Baud rates(
- LPUART peripheral supports Interrupts mode, DMA mode or pooled operation mode for transmitting/receiving the data using LPUART protocol or for detecting below listed errors while LPUART communication session is happening:
- Transmit data register empty and transmission complete.
- Receive data register full.
- Receive overrun, parity error, framing error, and noise error.
- Idle receivers detect.
- Active edge on receive pin.
- Break detect supporting LIN.
- Receive data match.
- S32K144 also supports hardware parity generation and checking to ensure the integrity of the data while LPUART communication is happening.
- It has Programmable LPUART data length of 7-10 bits and LPUART stop bits of 1-2 bits.
- S32K144 MCU has feature to use the LPUART peripheral to wake up the MCU (if it is programmed in sleep modes), it can be waked up in either of the 3 below mentioned events:
- Idle line wakeup
- Address mark wakeup
- Receive data match.
- Support of request to send (RTS) and clear to send (CTS) signals, for hardware flow control, example of hardware flow control is a half-duplex radio modem to computer interface.
- Support of IrDA 1.4 format with programmable pulse width for IR communication.
- LPUART peripheral of S32K144 supports independent FIFO buffer for transmission and receiving of Data.
- Also, LPUART peripheral FIFO of S32K144 has additional features like:
- configurable watermark (lowest number of bytes) for transmit and receive buffer, when watermark is achieved corresponding status is changed of LPUART peripheral.
- Option for receiver to assert request after a configurable number of idle.
characters if receive FIFO is not empty.
Tx and Rx FIFO in S32K144 for all LPUART Instances both are of 4 words size. 1 Word is 1 byte(8 bits). So FiFo size is 4 byte long(32 bits).
LPUART Hardware Pinout in S32K144 MCU
LPUART Pinout and Hardware Instances
LPUART peripheral in S32K144 has 3 instances: LPUART0, LPUART1, LPUART2.
All the LPUART Instances has 4 pins:
- RX: Receiving of data
- TX: Transmission of data
- CTS: Clear to Send pin for hardware flow control.
- RTS: Request to Send for hardware flow control.
S32K144 UART Pins
Each LPUART instance supports all the 4 pins, with below mentioned pin details.
In LPUART0 there are following number of pins:
- For RX pin (LPUART Function) there are 3 MCU Pins.
- For TX (LPUART Function) there are 3 MCU pins
- For CTS (LPUART Function) there are 2 MCU pins
- For RTS (LPUART Function) there are 2 MCU pins.
In LPUART1 there are following number of pins:
- For RX pin (LPUART Function) there are 3 MCU Pins.
- For TX (LPUART Function) there are 3 MCU pins
- For CTS (LPUART Function) there are 3 MCU pins
- For RTS (LPUART Function) there are 3 MCU pins.
In LPUART2 there are following number of pins:
- For RX pin (LPUART Function) there are 3 MCU Pins.
- For TX (LPUART Function) there are 3 MCU pins
- For CTS (LPUART Function) there are 3 MCU pins
- For RTS (LPUART Function) there are 3 MCU pins.
How to use LPUART Pins in S32K144 MCU for doing UART Communication?
Now for doing UART communication, we need to connect hardware UART pins of the MCU, for doing so follow the steps:
- At first select which instance of LPUART wanna use, once selected. As told above their are 3 instances of LPUART in S32K144 MCU.
- Once selected, then use above excel to short select which pin of corresponding LPUART has to be used.
- Lets say we use LPUART1 and use PTC7 and PTC6 as Tx & Rx pins of LPUART.
- So connect these pins of MCU with external UART Module.
- Remember Tx pin of MCU is connected to Rx pin of external UART Module and Rx pin of MCU is connected to Tx pin of external UART Module.
- Here i am going to use USB to serial FTDI connector with Original S32K144 evaluation2 board.
- With ElecronicsV2 board, it has on-board UART driver IC at LPUART1 PTC7 and PTC6 pins.
How to configure UART Peripheral in S32K144 using S32 Design Studio IDE
UART Peripheral of S32K144 MCU can be configured using the Peripheral configuration tools of S32 Design Studio. These tools provide us with the GUI interface to configure the UART Peripheral of the MCU. To know in detail about the Peripheral configuration of S32 Design Studio refer to these.
Go to perpheral view in S32 Configuration Tool
Then go to component view, where we can see different SDK modules for the correspodning S32 MCU.
Now we have to use LPUART, which is a peripheral of the MCU. So it would be having its driver files to use. So go to the Driver section and click on its + sign.
Here you can see list of all driver files, that are available. So search for lpuart and select it.
LPUART SDK for S32K144 MCU
LPUART SDK
S32K SDK/drivers provide an easy to use and quick way to use LPUART peripheral in S32K144, which is known as LPUART SDK.
Each S32 SDK driver can be configured and enabled to use in the project via S32 Configuration Tool. Will be digging into that part, in next section. For now, let’s understand the LPUART SDK in some detail, so as to use UART peripheral via LPUART.
In the SDK of LPUART there are header files and source files for LPUART Driver and LPUART Interrupt.
- LPUART interrupt files contains functions for using &configuring of LPUART interrupts and IRQ handler in S32K144 MCU.
- LPUART driver files contains functions for using/configuration of LPUART Peripheral.
LPUART Driver
LPUART driver files are further divided into LPUART Peripheral Abstraction Layer (PAL) & LPUART Low-level drivers., as shown below:
- LPUART Peripheral Abstraction Layer(PAL): contains functions and variables that are directly used in main.c or application code. And internally these functions use the LPUART Low-level drivers & LPUART IRQ . So if hardware is changed LPUART PAL would remain same and only internal low-level driver files need to be changed or modified. By this way we don’t have make many changes on application level.
- LPUART Low-level driver: contains functions that configures the LPUART peripheral registers for initializing the peripheral, using the peripheral and processing the data of peripheral at hardware level. These files are the ones which actually interacts with the hardware and make it configurable to our needs. 
In the blogs we will be exploring the LPUART Peripheral Abstraction Layer files (PAL) in more details, as that would be directly used in our application project development(main.c) and driver creation of UART modules (GPS, GSM, IoT Modules and etc)
LPUART PAL
In LPUART PAL there are 2 files lpuart_driver.c and lpuart_driver.h files.
Lets get into these files:
- lpuart_driver.h: contains the enums, structures and function declarations that would be used in application code. Only functions which are declared in this header file can be used in main.c or application project.
lpuart_driver.c: contains the function definations of the declared functions(uses the low-level driver functions) along with some static functions also that are restricted to use in this file only.
Functions
How to use LPUART PAL for doing UART Communication in S32K144 MCU.
- Features of LPUART PAL.
- Initialization and configuration API’s of UART peripheral using LPUART PAL.
- LPUART_DRV_Init: This function is the first function that has to be used in main.c to initialize the LPUART peripheral. This function is just like Serial.begin(9600) of Arduino IDE environment.
status_t LPUART_DRV_Init(uint32_t instance, lpuart_state_t * lpuartStatePtr,
const lpuart_user_config_t * lpuartUserConfig);
This function has 3 function parametrs as follows:
- instance: integer number indicating which instance of LPUART we are going to use.
- lpuart_user_config and lpuart_state_t: structure pointers have to be sent in this function as parameters. (For the info on these structures refers next section)
#define INST_LPUART_LPUART_1 1
extern lpuart_state_t lpUartState1;
/* External declaration of LPUART configuration structure */
extern const lpuart_user_config_t lpUartInitConfig1;
lpuart_state_t lpUartState1;
const lpuart_user_config_t lpUartInitConfig1 = {
.transferType = LPUART_USING_INTERRUPTS,
.baudRate = 9600UL,
.parityMode = LPUART_PARITY_DISABLED,
.stopBitCount = LPUART_ONE_STOP_BIT,
.bitCountPerChar = LPUART_8_BITS_PER_CHAR,
.rxDMAChannel = 0UL,
.txDMAChannel = 0UL
};
/* Initialize LPUART instance */
LPUART_DRV_Init(INST_LPUART_LPUART_1, &lpUartState1, &lpUartInitConfig1);
In LPUART PAL their are 3 ways by which we can send and receive data.
- Interrupt based
- DMA Based
- Pooling Based.
In this blog, we are going to explore and understand pooling based method and it’s API. As to use by interrupt and DMA based, we have to know about Interrupt and DMA. So we are going to cover Interrupt and DMA based LPUART communication under topics: Interrupts in S32K144 and DMA in S32K144 MCU.
What is pooling method in Embedded?
LPUART PAL API’s for doing pooling based communication
- LPUART_DRV_SendDataPolling
status_t LPUART_DRV_SendDataPolling(uint32_t instance, const uint8_t *txBuff, uint32_t txSize);
This function has 3 parametrs:
- instance: integer number indicating which instance of LPUART we are going to use.
- txBuff: buffer pointer, pointing to the data which needs to be send out.
- txSize: size of data that has to be sent.
/* Welcome message displayed at the console */
#define welcomeMsg "This example is an simple echo using LPUART\r\n\
it will send back any character you send to it.\r\n\
The board will greet you if you send 'Hello Board'\r\
\nNow you can begin typing:\r\n"
/* Send a welcome message */
LPUART_DRV_SendDataPolling(INST_LPUART_LPUART_1, (uint8_t *)welcomeMsg, strlen(welcomeMsg));
- LPUART_DRV_ReceiveDataPolling
status_t LPUART_DRV_ReceiveDataPolling(uint32_t instance, uint8_t *rxBuff, uint32_t rxSize);
This function has 3 function parameters:
- instance: integer number indicating which instance of LPUART we are going to use.
- rxBuff: buffer pointer, would be containing the received data.
- rxSize: size of data that has to be received.
/* Receive buffer size */
#define BUFFER_SIZE 256U
/* Buffer used to receive data from the console */
uint8_t buffer[BUFFER_SIZE];
LPUART_DRV_ReceiveDataPolling(INST_LPUART_LPUART_1, buffer, 1U);
Data Types
There are 2 structures that are important and will be used often
- lpuart_user_config_t: This structure has members to configure the LPUART according to user defined settings.
/*! @brief LPUART configuration structure
*
* Implements : lpuart_user_config_t_Class
*/
typedef struct
{
uint32_t baudRate; /*!< LPUART baud rate */
lpuart_parity_mode_t parityMode; /*!< parity mode, disabled (default), even, odd */
lpuart_stop_bit_count_t stopBitCount; /*!< number of stop bits, 1 stop bit (default) or 2 stop bits */
lpuart_bit_count_per_char_t bitCountPerChar; /*!< number of bits in a character (8-default, 9 or 10);
for 9/10 bits chars, users must provide appropriate buffers
to the send/receive functions (bits 8/9 in subsequent bytes);
for DMA transmission only 8-bit char is supported. */
lpuart_transfer_type_t transferType; /*!< Type of LPUART transfer (interrupt/dma based) */
uint8_t rxDMAChannel; /*!< Channel number for DMA rx channel.
If DMA mode isn't used this field will be ignored. */
uint8_t txDMAChannel; /*!< Channel number for DMA tx channel.
If DMA mode isn't used this field will be ignored. */
} lpuart_user_config_t;
/* External declaration of LPUART configuration structure */
extern const lpuart_user_config_t lpUartInitConfig1;
const lpuart_user_config_t lpUartInitConfig1 = {
.transferType = LPUART_USING_INTERRUPTS,
.baudRate = 9600UL,
.parityMode = LPUART_PARITY_DISABLED,
.stopBitCount = LPUART_ONE_STOP_BIT,
.bitCountPerChar = LPUART_8_BITS_PER_CHAR,
.rxDMAChannel = 0UL,
.txDMAChannel = 0UL
};
- lpuart_state_t: This structure has data members, which keep track of the on-going transfers .
/*!
* @brief Runtime state of the LPUART driver.
*
* Note that the caller provides memory for the driver state structures during
* initialization because the driver does not statically allocate memory.
*
* Implements : lpuart_state_t_Class
*/
typedef struct
{
const uint8_t * txBuff; /*!< The buffer of data being sent.*/
uint8_t * rxBuff; /*!< The buffer of received data.*/
volatile uint32_t txSize; /*!< The remaining number of bytes to be transmitted. */
volatile uint32_t rxSize; /*!< The remaining number of bytes to be received. */
volatile bool isTxBusy; /*!< True if there is an active transmit.*/
volatile bool isRxBusy; /*!< True if there is an active receive.*/
volatile bool isTxBlocking; /*!< True if transmit is blocking transaction. */
volatile bool isRxBlocking; /*!< True if receive is blocking transaction. */
lpuart_bit_count_per_char_t bitCountPerChar; /*!< number of bits in a char (8/9/10) */
uart_callback_t rxCallback; /*!< Callback to invoke for data receive
Note: when the transmission is interrupt based, the callback
is being called upon receiving a byte; when DMA transmission
is used, the bytes are copied to the rx buffer by the DMA engine
and the callback is called when all the bytes have been transferred. */
void * rxCallbackParam; /*!< Receive callback parameter pointer.*/
uart_callback_t txCallback; /*!< Callback to invoke for data send
Note: when the transmission is interrupt based, the callback
is being called upon sending a byte; when DMA transmission
is used, the bytes are copied to the tx buffer by the DMA engine
and the callback is called when all the bytes have been transferred. */
void * txCallbackParam; /*!< Transmit callback parameter pointer.*/
lpuart_transfer_type_t transferType; /*!< Type of LPUART transfer (interrupt/dma based) */
#if FEATURE_LPUART_HAS_DMA_ENABLE
uint8_t rxDMAChannel; /*!< DMA channel number for DMA-based rx. */
uint8_t txDMAChannel; /*!< DMA channel number for DMA-based tx. */
#endif
semaphore_t rxComplete; /*!< Synchronization object for blocking Rx timeout condition */
semaphore_t txComplete; /*!< Synchronization object for blocking Tx timeout condition */
volatile status_t transmitStatus; /*!< Status of last driver transmit operation */
volatile status_t receiveStatus; /*!< Status of last driver receive operation */
} lpuart_state_t;
extern lpuart_state_t lpUartState1;
lpuart_state_t lpUartState1;
UART Demo Code for S32K144 MCU
S32 SDK/provides as example demo on LPUART driver to demonstarate how to use the LPUART driver for UART communicatio protocol. Demo Example is named as: lpuart_echo_s32k144
/*
* Copyright 2020 NXP
* All rights reserved.
*
* NXP Confidential. This software is owned or controlled by NXP and may only be
* used strictly in accordance with the applicable license terms. By expressly
* accepting such terms or by downloading, installing, activating and/or otherwise
* using the software, you are agreeing that you have read, and that you agree to
* comply with and are bound by, such license terms. If you do not agree to be
* bound by the applicable license terms, then you may not retain, install,
* activate or otherwise use the software. The production use license in
* Section 2.3 is expressly granted for this software.
*/
/* ###################################################################
** Filename : main.c
** Project : lpuart_echo_s32k144
** Processor : S32K144
** Version : Driver 01.00
** Compiler : GNU C Compiler
** Date/Time : 2020-02-20, 12:27, # CodeGen: 1
** Abstract :
** Main module.
** This module contains user's application code.
** Settings :
** Contents :
** No public methods
**
** ###################################################################*/
/*!
** @file main.c
** @version 01.00
** @brief
** Main module.
** This module contains user's application code.
*/
/*!
** @addtogroup main_module main module documentation
** @{
*/
/* MODULE main */
/* Including needed modules to compile this module/procedure */
#include "sdk_project_config.h"
#include <stdio.h>
#include <string.h>
volatile int exit_code = 0;
/* Welcome message displayed at the console */
#define welcomeMsg "This example is an simple echo using LPUART\r\n\
it will send back any character you send to it.\r\n\
The board will greet you if you send 'Hello Board'\r\
\nNow you can begin typing:\r\n"
/* Error message displayed at the console, in case data is received erroneously */
#define errorMsg "An error occurred! The application will stop!\r\n"
/* Timeout in ms for blocking operations */
#define TIMEOUT 500U
/* Receive buffer size */
#define BUFFER_SIZE 256U
/* Buffer used to receive data from the console */
uint8_t buffer[BUFFER_SIZE];
uint8_t bufferIdx;
/* UART rx callback for continuous reception, byte by byte */
void rxCallback(void *driverState, uart_event_t event, void *userData)
{
/* Unused parameters */
(void)driverState;
(void)userData;
/* Check the event type */
if (event == UART_EVENT_RX_FULL)
{
/* The reception stops when newline is received or the buffer is full */
if ((buffer[bufferIdx] != '\n') && (bufferIdx != (BUFFER_SIZE - 2U)))
{
/* Update the buffer index and the rx buffer */
bufferIdx++;
LPUART_DRV_SetRxBuffer(INST_LPUART_LPUART_1, &buffer[bufferIdx], 1U);
}
}
}
/*!
\brief The main function for the project.
\details The startup initialization sequence is the following:
* - startup asm routine
* - main()
*/
int main(void)
{
/* Write your local variable definition here */
status_t status;
/* Declare a buffer used to store the received data */
uint32_t bytesRemaining;
/* Write your code here */
/* For example: for(;;) { } */
/* Initialize and configure clocks
* - see clock manager component for details
*/
CLOCK_SYS_Init(g_clockManConfigsArr, CLOCK_MANAGER_CONFIG_CNT,
g_clockManCallbacksArr, CLOCK_MANAGER_CALLBACK_CNT);
CLOCK_SYS_UpdateConfiguration(0U, CLOCK_MANAGER_POLICY_AGREEMENT);
/* Initialize pins
* - See PinSettings component for more info
*/
PINS_DRV_Init(NUM_OF_CONFIGURED_PINS0, g_pin_mux_InitConfigArr0);
/* Initialize LPUART instance */
LPUART_DRV_Init(INST_LPUART_LPUART_1, &lpUartState1, &lpUartInitConfig1);
/* Install the callback for rx events */
LPUART_DRV_InstallRxCallback(INST_LPUART_LPUART_1, rxCallback, NULL);
/* Send a welcome message */
LPUART_DRV_SendDataBlocking(INST_LPUART_LPUART_1, (uint8_t *)welcomeMsg, strlen(welcomeMsg), TIMEOUT);
/* Infinite loop:
* - Receive data from user
* - Echo the received data back
*/
while (1)
{
/* Receive and store data byte by byte until new line character is received,
* or the buffer becomes full (256 characters received)
*/
LPUART_DRV_ReceiveData(INST_LPUART_LPUART_1, buffer, 1U);
/* Wait for transfer to be completed */
while(LPUART_DRV_GetReceiveStatus(INST_LPUART_LPUART_1, &bytesRemaining) == STATUS_BUSY);
/* Check the status */
status = LPUART_DRV_GetReceiveStatus(INST_LPUART_LPUART_1, &bytesRemaining);
if (status != STATUS_SUCCESS)
{
/* If an error occurred, send the error message and exit the loop */
LPUART_DRV_SendDataBlocking(INST_LPUART_LPUART_1, (uint8_t *)errorMsg, strlen(errorMsg), TIMEOUT);
break;
}
/* Append string terminator to the received data */
bufferIdx++;
buffer[bufferIdx] = 0U;
/* If the received string is "Hello Board", send back "Hello World" */
if(strcmp((char *)buffer, "Hello Board\n") == 0)
{
strcpy((char *)buffer, "Hello World\n");
}
/* Send the received data back */
LPUART_DRV_SendDataBlocking(INST_LPUART_LPUART_1, buffer, bufferIdx, TIMEOUT);
/* Reset the buffer index to start a new reception */
bufferIdx = 0U;
}
for(;;) {
if(exit_code != 0) {
break;
}
}
return exit_code;
} /*** End of main routine. DO NOT MODIFY THIS TEXT!!! ***/
/* END main */
/*!
** @}
*/
lpuart_echo_s32k144 demo code explanation:
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UART Peripheral in S32K144
Introduction –> UART Peripheral is one of the most common communication modules present in every series of microcontrollers. For Crisp and Short UART understanding as a concept, redirect yourself to this BLOG, it might take a couple of minutes to have an overlayed understanding. Now, UART is used in GPS modules or other wireless modules like Bluetooth and WiFi. GPS Modules- Use UART to exchange NMEA strings for positioning data. Bluetooth (e.g., HC-05)- Employs UART for wireless data transfer and pairing. Wi-Fi Modules (e.g., ESP8266, ESP32)- Use UART for sending AT commands and receiving responses. –> In S32K144, we’ll be referring to the UART as LPUART because the UART supported in S32K144 is a low-power UART called LPUART(Low Power Universal Asynchronous Receiver/Transmitter). –> NOTE: A single instance of UART contains a pair of a TX pin and an RX pin. –> Below are mentioned table of LPUART instances supported in different series with highlighted sections of our development board: Features of UART > Full-Duplex, standard Non-Return-to-Zero (NRZ) format Full-duplex: Communication happens in both directions at the same time. One device can send data while receiving data simultaneously. Yes, as you might be thinking about Half-Duplex Communication and it also exists where the channel can either send or receive data, but not both at the same time. At the same time, there also exists a last type of this which you might not think, that is Simplex Communication where only one-way communication is possible. Standard Non-Return-to-Zero (NRZ) Format: Data is represented as high (1) or low (0) voltage levels. Voltage doesn’t return to zero between bits, ensuring efficient use of the signal without gaps. > Programmable baud rates (13-bit modulo divider) Baud Rate: The baud rate is the number of signal changes or symbols transmitted per second in a communication system. For example, a baud rate of 9600 means 9600 bits are sent every second. Baud Rate in LPUART: In LPUART, a 13-bit counter generates the baud rate by dividing the LPUART clock. The division factor is set using the BAUD[SBR] register, with values ranging from 1 to 8191. The baud rate generator is always active when the transmitter or receiver is enabled, and for the transmitter, each character aligns with the next edge of the transmit bit clock. This ensures continuous operation despite minor errors. But there’s a catch that you might see in development, our IDE only gives some preset group of baud rates like 4800, 9600, 19200, 38400, 57600, 115200, 230400, 460800, and 921600, then “what is the use of this baud-rate generator?”. The generator’s role is to provide flexibility to derive these preset baud rates from the main LPUART clock. While only specific baud rates may be officially supported (due to hardware limits or design constraints), the generator’s configuration ensures these values can be accurately achieved by adjusting the divisor (SBR) and oversampling ratio (OSR), which improves accuracy by sampling each bit multiple times. We’ll be discussing the sampling technique in a further section. > Transmission Functionality Now, we’ll be learning how characters are sent over LPUART where we’ll also learn different other features of LPUART. Below mentioned is the Block Diagram of LPUART Transmission: No need to worry by viewing this block diagram, after this go-through you’ll be able to teach others about this block diagram seamlessly. Idle State and Configuration: The transmitter output (TXD) is idle at a logic high by default. To invert this behavior, set the CTRL[TXINV] bit. The transmitter is enabled by setting CTRL[TE], which queues a preamble (idle state) character. Data Transmission: Data is written to the transmit buffer via the DATA register. The transmit shift register (9–13 bits long based on configuration) sends a start bit, data bits, and a stop bit. In 8-bit mode, the shift register handles 1 start bit, 8 data bits, and 1 stop bit. Operation Flow: When the shift register is free, it fetches data from the transmit buffer and synchronizes it with the baud rate clock. The STAT[TDRE] flag is set, indicating readiness for new data. If no new data is available after sending the stop bit, the transmitter enters idle mode (TXD high). Disabling the Transmitter: Writing 0 CTRL[TE] doesn’t stop the transmitter immediately. Current activity (data, idle, or break character) must finish first. Sending Break and Queued Idle in LPUART(Feature offered by LPUART)–> Sending break and queued idle refers to transmitting a break character (a full character of logic 0) or an idle character (logic 1) to manage communication flow, often to signal the end of a message or to wake up sleeping receivers. These actions can be queued by setting control bits in the LPUART, ensuring proper synchronization and transmission. Break Characters: A break character forces the TX line to logic 0 for a full character time (9–12 bits, including start and stop bits). For a longer 13-bit break, set STAT[BRK13]. To send a break: Wait for STAT[TDRE] (Transmit Data Register Empty) to ensure the last character has been shifted out. Set CTRL[SBK] to 1, then clear it to 0. This queues a break for transmission. If CTRL[SBK] remains 1, additional break characters will be queued automatically. Break characters received on RX are detected as all 0s with a framing error (STAT[FE] = 1). Alternative Break Transmission: Writing to DATA with bit 13 set and all data bits cleared can send a break as part of the data stream. This method also works with DMA to transmit a break character. Idle Characters: An idle character (logic 1 for a full character time) can wake up sleeping receivers during idle-line wakeup. To send an idle character: Wait for STAT[TDRE]. Clear and then set CTRL[TE]. This queues an idle character. The transmitter holds TXD high until the queued idle is sent. Alternative Idle Transmission: Writing to DATA with bit 13 and all data bits set can send an idle character as part of the data stream. DMA can also be used for idle transmission. Control Bits for Break Length: The length of break characters depends
Author: Kunal Gupta
