USART - Synchronous/Asynchronous Serial
Description
Universal Synchronous/Asynchronous Receiver/Transmitter Peripheral API.
The Universal Synchronous/Asynchronous Receiver/Transmitter (USART) is a very flexible serial I/O module. It supports full duplex asynchronous UART communication as well as RS-485, SPI, MicroWire, and 3-wire. It can also interface with ISO7816 Smart-Cards, and IrDA devices.
The USART has a wide selection of operating modes, frame formats, and baud rates. All features are supported through the API of this module.
Triple buffering and DMA support makes high data-rates possible with minimal CPU intervention. It is possible to transmit and receive large frames while the MCU remains in EM1 Sleep.
This module does not support DMA configuration. The UARTDRV and SPIDRV drivers provide full support for DMA and more.
The following steps are necessary for basic operation:
Clock enable:
To initialize the USART for asynchronous operation (e.g., UART):
To initialize the USART for synchronous operation (e.g., SPI):
After pins are assigned for the application/board, enable pins at the desired location. Available locations can be obtained from the Pin Definitions section in the data sheet.
- Note
- UART hardware flow control is not directly supported in hardware on _SILICON_LABS_32B_SERIES_0 parts.
- UARTDRV supports all types of UART flow control. Software assisted hardware flow control is available for parts without true UART hardware flow control.
Data Structures |
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struct | USART_InitAsync_TypeDef |
Asynchronous mode initialization structure.
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struct | USART_PrsTriggerInit_TypeDef |
USART PRS trigger enable.
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struct | USART_InitSync_TypeDef |
Synchronous mode initialization structure.
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struct | USART_InitIrDA_TypeDef |
IrDA mode initialization structure.
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struct | USART_InitI2s_TypeDef |
I2S mode initialization structure.
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Functions |
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void | USART_BaudrateAsyncSet (USART_TypeDef *usart, uint32_t refFreq, uint32_t baudrate, USART_OVS_TypeDef ovs) |
Configure USART/UART operating in asynchronous mode to use a given baudrate (or as close as possible to a specified baudrate).
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uint32_t | USART_BaudrateCalc (uint32_t refFreq, uint32_t clkdiv, bool syncmode, USART_OVS_TypeDef ovs) |
Calculate baudrate for USART/UART given reference frequency, clock division, and oversampling rate (if async mode).
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uint32_t | USART_BaudrateGet (USART_TypeDef *usart) |
Get the current baudrate for USART/UART.
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void | USART_BaudrateSyncSet (USART_TypeDef *usart, uint32_t refFreq, uint32_t baudrate) |
Configure the USART operating in synchronous mode to use a given baudrate (or as close as possible to a specified baudrate).
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void | USART_Enable (USART_TypeDef *usart, USART_Enable_TypeDef enable) |
Enable/disable USART/UART receiver and/or transmitter.
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void | USART_InitAsync (USART_TypeDef *usart, const USART_InitAsync_TypeDef *init) |
Initialize USART/UART for normal asynchronous mode.
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void | USART_InitSync (USART_TypeDef *usart, const USART_InitSync_TypeDef *init) |
Initialize USART for synchronous mode.
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void | USARTn_InitIrDA (USART_TypeDef *usart, const USART_InitIrDA_TypeDef *init) |
Initialize USART for asynchronous IrDA mode.
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void | USART_InitI2s (USART_TypeDef *usart, USART_InitI2s_TypeDef *init) |
Initialize USART for I2S mode.
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void | USART_InitPrsTrigger (USART_TypeDef *usart, const USART_PrsTriggerInit_TypeDef *init) |
Initialize the automatic transmissions using PRS channel as a trigger.
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void | USART_IntClear (USART_TypeDef *usart, uint32_t flags) |
Clear one or more pending USART interrupts.
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void | USART_IntDisable (USART_TypeDef *usart, uint32_t flags) |
Disable one or more USART interrupts.
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void | USART_IntEnable (USART_TypeDef *usart, uint32_t flags) |
Enable one or more USART interrupts.
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uint32_t | USART_IntGet (USART_TypeDef *usart) |
Get pending USART interrupt flags.
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uint32_t | USART_IntGetEnabled (USART_TypeDef *usart) |
Get enabled and pending USART interrupt flags.
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void | USART_IntSet (USART_TypeDef *usart, uint32_t flags) |
Set one or more pending USART interrupts from SW.
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uint32_t | USART_StatusGet (USART_TypeDef *usart) |
Get USART STATUS register.
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void | USART_Reset (USART_TypeDef *usart) |
Reset USART/UART to the same state that it was in after a hardware reset.
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uint8_t | USART_Rx (USART_TypeDef *usart) |
Receive one 4-8 bit frame, (or part of 10-16 bit frame).
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uint16_t | USART_RxDouble (USART_TypeDef *usart) |
Receive two 4-8 bit frames or one 10-16 bit frame.
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uint32_t | USART_RxDoubleExt (USART_TypeDef *usart) |
Receive two 4-9 bit frames, or one 10-16 bit frame with extended information.
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uint16_t | USART_RxExt (USART_TypeDef *usart) |
Receive one 4-9 bit frame (or part of 10-16 bit frame) with extended information.
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uint8_t | USART_RxDataGet (USART_TypeDef *usart) |
Receive one 4-8 bit frame, (or part of 10-16 bit frame).
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uint16_t | USART_RxDoubleGet (USART_TypeDef *usart) |
Receive two 4-8 bit frames, or one 10-16 bit frame.
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uint32_t | USART_RxDoubleXGet (USART_TypeDef *usart) |
Receive two 4-9 bit frames, or one 10-16 bit frame with extended information.
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uint16_t | USART_RxDataXGet (USART_TypeDef *usart) |
Receive one 4-9 bit frame, (or part of 10-16 bit frame) with extended information.
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uint8_t | USART_SpiTransfer (USART_TypeDef *usart, uint8_t data) |
Perform one 8 bit frame SPI transfer.
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void | USART_Tx (USART_TypeDef *usart, uint8_t data) |
Transmit one 4-9 bit frame.
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void | USART_TxDouble (USART_TypeDef *usart, uint16_t data) |
Transmit two 4-9 bit frames or one 10-16 bit frame.
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void | USART_TxDoubleExt (USART_TypeDef *usart, uint32_t data) |
Transmit two 4-9 bit frames or one 10-16 bit frame with extended control.
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void | USART_TxExt (USART_TypeDef *usart, uint16_t data) |
Transmit one 4-9 bit frame with extended control.
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Macros |
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#define | USART_INITASYNC_DEFAULT |
Default configuration for USART asynchronous initialization structure.
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#define | USART_INITPRSTRIGGER_DEFAULT |
Default configuration for USART PRS triggering structure.
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#define | USART_INITSYNC_DEFAULT |
Default configuration for USART sync initialization structure.
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#define | USART_INITIRDA_DEFAULT |
Default configuration for IrDA mode initialization structure.
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#define | USART_INITI2S_DEFAULT |
Default configuration for I2S mode initialization structure.
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Typedefs |
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typedef uint8_t | USART_PRS_Channel_t |
PRS Channel type.
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Enumerations |
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enum |
USART_Databits_TypeDef
{
usartDatabits4 = USART_FRAME_DATABITS_FOUR, usartDatabits5 = USART_FRAME_DATABITS_FIVE, usartDatabits6 = USART_FRAME_DATABITS_SIX, usartDatabits7 = USART_FRAME_DATABITS_SEVEN, usartDatabits8 = USART_FRAME_DATABITS_EIGHT, usartDatabits9 = USART_FRAME_DATABITS_NINE, usartDatabits10 = USART_FRAME_DATABITS_TEN, usartDatabits11 = USART_FRAME_DATABITS_ELEVEN, usartDatabits12 = USART_FRAME_DATABITS_TWELVE, usartDatabits13 = USART_FRAME_DATABITS_THIRTEEN, usartDatabits14 = USART_FRAME_DATABITS_FOURTEEN, usartDatabits15 = USART_FRAME_DATABITS_FIFTEEN, usartDatabits16 = USART_FRAME_DATABITS_SIXTEEN } |
Databit selection.
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enum |
USART_Enable_TypeDef
{
usartDisable = 0x0, usartEnableRx = USART_CMD_RXEN, usartEnableTx = USART_CMD_TXEN, usartEnable = (USART_CMD_RXEN | USART_CMD_TXEN) } |
Enable selection.
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enum |
USART_OVS_TypeDef
{
usartOVS16 = USART_CTRL_OVS_X16, usartOVS8 = USART_CTRL_OVS_X8, usartOVS6 = USART_CTRL_OVS_X6, usartOVS4 = USART_CTRL_OVS_X4 } |
Oversampling selection, used for asynchronous operation.
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enum |
USART_Parity_TypeDef
{
usartNoParity = USART_FRAME_PARITY_NONE, usartEvenParity = USART_FRAME_PARITY_EVEN, usartOddParity = USART_FRAME_PARITY_ODD } |
Parity selection, mainly used for asynchronous operation.
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enum |
USART_Stopbits_TypeDef
{
usartStopbits0p5 = USART_FRAME_STOPBITS_HALF, usartStopbits1 = USART_FRAME_STOPBITS_ONE, usartStopbits1p5 = USART_FRAME_STOPBITS_ONEANDAHALF, usartStopbits2 = USART_FRAME_STOPBITS_TWO } |
Stop bits selection, used for asynchronous operation.
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enum |
USART_ClockMode_TypeDef
{
usartClockMode0 = USART_CTRL_CLKPOL_IDLELOW | USART_CTRL_CLKPHA_SAMPLELEADING, usartClockMode1 = USART_CTRL_CLKPOL_IDLELOW | USART_CTRL_CLKPHA_SAMPLETRAILING, usartClockMode2 = USART_CTRL_CLKPOL_IDLEHIGH | USART_CTRL_CLKPHA_SAMPLELEADING, usartClockMode3 = USART_CTRL_CLKPOL_IDLEHIGH | USART_CTRL_CLKPHA_SAMPLETRAILING } |
Clock polarity/phase mode.
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enum |
USART_IrDAPw_Typedef
{
usartIrDAPwONE = USART_IRCTRL_IRPW_ONE, usartIrDAPwTWO = USART_IRCTRL_IRPW_TWO, usartIrDAPwTHREE = USART_IRCTRL_IRPW_THREE, usartIrDAPwFOUR = USART_IRCTRL_IRPW_FOUR } |
Pulse width selection for IrDA mode.
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enum |
USART_I2sFormat_TypeDef
{
usartI2sFormatW32D32 = USART_I2SCTRL_FORMAT_W32D32, usartI2sFormatW32D24M = USART_I2SCTRL_FORMAT_W32D24M, usartI2sFormatW32D24 = USART_I2SCTRL_FORMAT_W32D24, usartI2sFormatW32D16 = USART_I2SCTRL_FORMAT_W32D16, usartI2sFormatW32D8 = USART_I2SCTRL_FORMAT_W32D8, usartI2sFormatW16D16 = USART_I2SCTRL_FORMAT_W16D16, usartI2sFormatW16D8 = USART_I2SCTRL_FORMAT_W16D8, usartI2sFormatW8D8 = USART_I2SCTRL_FORMAT_W8D8 } |
I2S format selection.
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enum |
USART_I2sJustify_TypeDef
{
usartI2sJustifyLeft = USART_I2SCTRL_JUSTIFY_LEFT, usartI2sJustifyRight = USART_I2SCTRL_JUSTIFY_RIGHT } |
I2S frame data justify.
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Function Documentation
◆ USART_BaudrateAsyncSet()
void USART_BaudrateAsyncSet | ( | USART_TypeDef * |
usart,
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uint32_t |
refFreq,
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uint32_t |
baudrate,
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USART_OVS_TypeDef |
ovs
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Configure USART/UART operating in asynchronous mode to use a given baudrate (or as close as possible to a specified baudrate).
- Parameters
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[in] usart
A pointer to the USART/UART peripheral register block. [in] refFreq
USART/UART reference clock frequency in Hz. If set to 0, the currently configured reference clock is assumed. [in] baudrate
Baudrate to try to achieve for USART/UART. [in] ovs
Oversampling to be used. Normal is 16x oversampling but lower oversampling may be used to achieve higher rates or better baudrate accuracy in some cases. Notice that lower oversampling frequency makes the channel more vulnerable to bit faults during reception due to clock inaccuracies compared to the link partner.
◆ USART_BaudrateCalc()
uint32_t USART_BaudrateCalc | ( | uint32_t |
refFreq,
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uint32_t |
clkdiv,
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bool |
syncmode,
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USART_OVS_TypeDef |
ovs
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Calculate baudrate for USART/UART given reference frequency, clock division, and oversampling rate (if async mode).
This function returns the baudrate that a USART/UART module will use if configured with the given frequency, clock divisor, and mode. Notice that this function will not use the hardware configuration. It can be used to determine if a given configuration is sufficiently accurate for the application.
- Parameters
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[in] refFreq
USART/UART HF peripheral frequency used. [in] clkdiv
A clock division factor to be used. [in] syncmode
- True - synchronous mode operation.
- False - asynchronous mode operation.
[in] ovs
Oversampling used if in asynchronous mode. Not used if syncmode
is true.
- Returns
- Baudrate with given settings.
◆ USART_BaudrateGet()
uint32_t USART_BaudrateGet | ( | USART_TypeDef * |
usart
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Get the current baudrate for USART/UART.
This function returns the actual baudrate (not considering oscillator inaccuracies) used by a USART/UART peripheral.
- Parameters
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[in] usart
A pointer to the USART/UART peripheral register block.
- Returns
- The current baudrate.
◆ USART_BaudrateSyncSet()
void USART_BaudrateSyncSet | ( | USART_TypeDef * |
usart,
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uint32_t |
refFreq,
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uint32_t |
baudrate
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Configure the USART operating in synchronous mode to use a given baudrate (or as close as possible to a specified baudrate).
The configuration will be set to use a baudrate <= the specified baudrate to ensure that the baudrate does not exceed the specified value.
The fractional clock division is suppressed, although the hardware design allows it. It could cause half clock cycles to exceed a specified limit and thus potentially violate specifications for the slave device. In some special situations, a fractional clock division may be useful even in synchronous mode, but in those cases it must be directly adjusted, possibly assisted by USART_BaudrateCalc() :
- Parameters
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[in] usart
A pointer to the USART peripheral register block. (Cannot be used on UART modules.) [in] refFreq
A USART reference clock frequency in Hz that will be used. If set to 0, the currently-configured reference clock is assumed. [in] baudrate
Baudrate to try to achieve for USART.
◆ USART_Enable()
void USART_Enable | ( | USART_TypeDef * |
usart,
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USART_Enable_TypeDef |
enable
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Enable/disable USART/UART receiver and/or transmitter.
Notice that this function does not do any configuration. Enabling should normally be done after initialization (if not enabled as part of initialization).
- Parameters
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[in] usart
A pointer to the USART/UART peripheral register block. [in] enable
Select the status for the receiver/transmitter.
◆ USART_InitAsync()
void USART_InitAsync | ( | USART_TypeDef * |
usart,
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const USART_InitAsync_TypeDef * |
init
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Initialize USART/UART for normal asynchronous mode.
This function will configure basic settings to operate in normal asynchronous mode.
A special control setup not covered by this function must be done after using this function by direct modification of the CTRL register.
Notice that pins used by the USART/UART module must be properly configured by the user explicitly for the USART/UART to work as intended. (When configuring pins, remember to consider the sequence of configuration to avoid unintended pulses/glitches on output pins.)
- Parameters
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[in] usart
A pointer to the USART/UART peripheral register block. [in] init
A pointer to the initialization structure used to configure the basic async setup.
◆ USART_InitSync()
void USART_InitSync | ( | USART_TypeDef * |
usart,
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const USART_InitSync_TypeDef * |
init
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Initialize USART for synchronous mode.
This function will configure basic settings to operate in synchronous mode.
A special control setup not covered by this function must be done after using this function by direct modification of the CTRL register.
Notice that pins used by the USART module must be properly configured by the user explicitly for the USART to work as intended. (When configuring pins remember to consider the sequence of configuration to avoid unintended pulses/glitches on output pins.)
- Parameters
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[in] usart
A pointer to the USART peripheral register block. (UART does not support this mode.) [in] init
A pointer to the initialization structure used to configure basic async setup.
◆ USARTn_InitIrDA()
void USARTn_InitIrDA | ( | USART_TypeDef * |
usart,
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const USART_InitIrDA_TypeDef * |
init
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Initialize USART for asynchronous IrDA mode.
This function will configure basic settings to operate in asynchronous IrDA mode.
A special control setup not covered by this function must be done after using this function by direct modification of the CTRL and IRCTRL registers.
Notice that pins used by the USART/UART module must be properly configured by the user explicitly for the USART/UART to work as intended. (When configuring pins, remember to consider the sequence of configuration to avoid unintended pulses/glitches on output pins.)
- Parameters
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[in] usart
A pointer to the USART peripheral register block. [in] init
A pointer to the initialization structure used to configure async IrDA setup.
- Note
- Not all USART instances support IrDA. See the data sheet for your device.
◆ USART_InitI2s()
void USART_InitI2s | ( | USART_TypeDef * |
usart,
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USART_InitI2s_TypeDef * |
init
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Initialize USART for I2S mode.
This function will configure basic settings to operate in I2S mode.
A special control setup not covered by this function must be done after using this function by direct modification of the CTRL and I2SCTRL registers.
Notice that pins used by the USART module must be properly configured by the user explicitly for the USART to work as intended. (When configuring pins, remember to consider the sequence of configuration to avoid unintended pulses/glitches on output pins.)
- Parameters
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[in] usart
A pointer to the USART peripheral register block. (UART does not support this mode.) [in] init
A pointer to the initialization structure used to configure the basic I2S setup.
- Note
- This function does not apply to all USART's. See the chip Reference Manual.
◆ USART_InitPrsTrigger()
void USART_InitPrsTrigger | ( | USART_TypeDef * |
usart,
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const USART_PrsTriggerInit_TypeDef * |
init
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Initialize the automatic transmissions using PRS channel as a trigger.
- Note
- Initialize USART with USART_Init() before setting up the PRS configuration.
- Parameters
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[in] usart
A pointer to USART to configure. [in] init
A pointer to the initialization structure.
◆ USART_IntClear()
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