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:

#if !defined(_SILICON_LABS_32B_SERIES_2)
/* USART is a HFPERCLK peripheral. Enable HFPERCLK domain and USART0.
* We also need to enable the clock for GPIO to configure pins. */
CMU_ClockEnable (cmuClock_HFPER, true );
#endif

To initialize the USART for asynchronous operation (e.g., UART):

/* Initialize with default settings and then update fields according to application requirements. */
initAsync. baudrate = 38400;
USART_InitAsync (USART0, &initAsync);

To initialize the USART for synchronous operation (e.g., SPI):

/* Initialize with default settings and then update fields according to application requirements. */
/* Operate as SPI master */
initSync. master = true ;
/* Clock idle low, sample on falling edge. */
USART_InitSync (USART0, &initSync);

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
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

struct USART_InitAsync_TypeDef
Asynchronous mode initialization structure.
struct USART_PrsTriggerInit_TypeDef
USART PRS trigger enable.
struct USART_InitSync_TypeDef
Synchronous mode initialization structure.
struct USART_InitIrDA_TypeDef
IrDA mode initialization structure.
struct USART_InitI2s_TypeDef
I2S mode initialization structure.

Functions

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).
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).
uint32_t USART_BaudrateGet (USART_TypeDef *usart)
Get the current baudrate for USART/UART.
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).
void USART_Enable (USART_TypeDef *usart, USART_Enable_TypeDef enable)
Enable/disable USART/UART receiver and/or transmitter.
void USART_InitAsync (USART_TypeDef *usart, const USART_InitAsync_TypeDef *init)
Initialize USART/UART for normal asynchronous mode.
void USART_InitSync (USART_TypeDef *usart, const USART_InitSync_TypeDef *init)
Initialize USART for synchronous mode.
void USARTn_InitIrDA (USART_TypeDef *usart, const USART_InitIrDA_TypeDef *init)
Initialize USART for asynchronous IrDA mode.
void USART_InitI2s (USART_TypeDef *usart, USART_InitI2s_TypeDef *init)
Initialize USART for I2S mode.
void USART_InitPrsTrigger (USART_TypeDef *usart, const USART_PrsTriggerInit_TypeDef *init)
Initialize the automatic transmissions using PRS channel as a trigger.
void USART_IntClear (USART_TypeDef *usart, uint32_t flags)
Clear one or more pending USART interrupts.
void USART_IntDisable (USART_TypeDef *usart, uint32_t flags)
Disable one or more USART interrupts.
void USART_IntEnable (USART_TypeDef *usart, uint32_t flags)
Enable one or more USART interrupts.
uint32_t USART_IntGet (USART_TypeDef *usart)
Get pending USART interrupt flags.
uint32_t USART_IntGetEnabled (USART_TypeDef *usart)
Get enabled and pending USART interrupt flags.
void USART_IntSet (USART_TypeDef *usart, uint32_t flags)
Set one or more pending USART interrupts from SW.
uint32_t USART_StatusGet (USART_TypeDef *usart)
Get USART STATUS register.
void USART_Reset (USART_TypeDef *usart)
Reset USART/UART to the same state that it was in after a hardware reset.
uint8_t USART_Rx (USART_TypeDef *usart)
Receive one 4-8 bit frame, (or part of 10-16 bit frame).
uint16_t USART_RxDouble (USART_TypeDef *usart)
Receive two 4-8 bit frames or one 10-16 bit frame.
uint32_t USART_RxDoubleExt (USART_TypeDef *usart)
Receive two 4-9 bit frames, or one 10-16 bit frame with extended information.
uint16_t USART_RxExt (USART_TypeDef *usart)
Receive one 4-9 bit frame (or part of 10-16 bit frame) with extended information.
uint8_t USART_RxDataGet (USART_TypeDef *usart)
Receive one 4-8 bit frame, (or part of 10-16 bit frame).
uint16_t USART_RxDoubleGet (USART_TypeDef *usart)
Receive two 4-8 bit frames, or one 10-16 bit frame.
uint32_t USART_RxDoubleXGet (USART_TypeDef *usart)
Receive two 4-9 bit frames, or one 10-16 bit frame with extended information.
uint16_t USART_RxDataXGet (USART_TypeDef *usart)
Receive one 4-9 bit frame, (or part of 10-16 bit frame) with extended information.
uint8_t USART_SpiTransfer (USART_TypeDef *usart, uint8_t data)
Perform one 8 bit frame SPI transfer.
void USART_Tx (USART_TypeDef *usart, uint8_t data)
Transmit one 4-9 bit frame.
void USART_TxDouble (USART_TypeDef *usart, uint16_t data)
Transmit two 4-9 bit frames or one 10-16 bit frame.
void USART_TxDoubleExt (USART_TypeDef *usart, uint32_t data)
Transmit two 4-9 bit frames or one 10-16 bit frame with extended control.
void USART_TxExt (USART_TypeDef *usart, uint16_t data)
Transmit one 4-9 bit frame with extended control.

Macros

#define USART_INITASYNC_DEFAULT
Default configuration for USART asynchronous initialization structure.
#define USART_INITPRSTRIGGER_DEFAULT
Default configuration for USART PRS triggering structure.
#define USART_INITSYNC_DEFAULT
Default configuration for USART sync initialization structure.
#define USART_INITIRDA_DEFAULT
Default configuration for IrDA mode initialization structure.
#define USART_INITI2S_DEFAULT
Default configuration for I2S mode initialization structure.

Typedefs

typedef uint8_t USART_PRS_Channel_t
PRS Channel type.

Enumerations

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.
enum USART_Enable_TypeDef {
usartDisable = 0x0,
usartEnableRx = USART_CMD_RXEN,
usartEnableTx = USART_CMD_TXEN,
usartEnable = (USART_CMD_RXEN | USART_CMD_TXEN)
}
Enable selection.
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.
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.
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.
enum USART_HwFlowControl_TypeDef {
usartHwFlowControlNone = 0,
usartHwFlowControlCts ,
usartHwFlowControlRts ,
usartHwFlowControlCtsAndRts
}
Hardware Flow Control Selection.
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.
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.
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.
enum USART_I2sJustify_TypeDef {
usartI2sJustifyLeft = USART_I2SCTRL_JUSTIFY_LEFT,
usartI2sJustifyRight = USART_I2SCTRL_JUSTIFY_RIGHT
}
I2S frame data justify.

Function Documentation

USART_BaudrateAsyncSet()

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).

Parameters
[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,
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).

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
[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 )

Get the current baudrate for USART/UART.

This function returns the actual baudrate (not considering oscillator inaccuracies) used by a USART/UART peripheral.

Parameters
[in] usart A pointer to the USART/UART peripheral register block.
Returns
The current baudrate.

USART_BaudrateSyncSet()

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).

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
[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,
USART_Enable_TypeDef enable
)

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
[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,
const USART_InitAsync_TypeDef * init
)

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
[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,
const USART_InitSync_TypeDef * init
)

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
[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,
const USART_InitIrDA_TypeDef * init
)

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
[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,
USART_InitI2s_TypeDef * init
)

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
[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,
const USART_PrsTriggerInit_TypeDef * init
)

Initialize the automatic transmissions using PRS channel as a trigger.

Note
Initialize USART with USART_Init() before setting up the PRS configuration.
Parameters
[in] usart A pointer to USART to configure.
[in] init A pointer to the initialization structure.

USART_IntClear()

void USART_IntClear ( USART_TypeDef * usart,
uint32_t flags
)
inline

Clear one or more pending USART interrupts.

Parameters
[in] usart Pointer to USART/UART peripheral register block.
[in] flags Pending USART/UART interrupt source(s) to clear. Use one or more valid interrupt flags for the USART module (USART_IF_nnn) OR'ed together.

USART_IntDisable()

void USART_IntDisable ( USART_TypeDef * usart,
uint32_t flags
)
inline

Disable one or more USART interrupts.

Parameters
[in] usart Pointer to USART/UART peripheral register block.
[in] flags USART/UART interrupt source(s) to disable. Use one or more valid interrupt flags for the USART module (USART_IF_nnn) OR'ed together.

USART_IntEnable()

void USART_IntEnable ( USART_TypeDef * usart,
uint32_t flags
)
inline

Enable one or more USART interrupts.

Note
Depending on the use, a pending interrupt may already be set prior to enabling the interrupt. To ignore a pending interrupt, consider using USART_IntClear() prior to enabling the interrupt.
Parameters
[in] usart Pointer to USART/UART peripheral register block.
[in] flags USART/UART interrupt source(s) to enable. Use one or more valid interrupt flags for the USART module (USART_IF_nnn) OR'ed together.

USART_IntGet()

uint32_t USART_IntGet ( USART_TypeDef * usart )
inline

Get pending USART interrupt flags.

Note
The event bits are not cleared by the use of this function.
Parameters
[in] usart Pointer to USART/UART peripheral register block.
Returns
USART/UART interrupt source(s) pending. Returns one or more valid interrupt flags for the USART module (USART_IF_nnn) OR'ed together.

USART_IntGetEnabled()

uint32_t USART_IntGetEnabled ( USART_TypeDef * usart )
inline

Get enabled and pending USART interrupt flags.

Useful for handling more interrupt sources in the same interrupt handler.

Parameters
[in] usart Pointer to USART/UART peripheral register block.
Note
Interrupt flags are not cleared by the use of this function.
Returns
Pending and enabled USART interrupt sources. The return value is the bitwise AND combination of
  • the OR combination of enabled interrupt sources in USARTx_IEN_nnn register (USARTx_IEN_nnn) and
  • the OR combination of valid interrupt flags of the USART module (USARTx_IF_nnn).

USART_IntSet()

void USART_IntSet ( USART_TypeDef * usart,
uint32_t flags
)
inline

Set one or more pending USART interrupts from SW.

Parameters
[in] usart Pointer to USART/UART peripheral register block.
[in] flags USART/UART interrupt source(s) to set to pending. Use one or more valid interrupt flags for the USART module (USART_IF_nnn) OR'ed together.

USART_StatusGet()

uint32_t USART_StatusGet ( USART_TypeDef * usart )
inline

Get USART STATUS register.