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. */
#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.

/* Enable I/O and set location */
USART0->ROUTE = USART_ROUTE_RXPEN | USART_ROUTE_TXPEN | USER_LOCATION;
/* Also enable CS and CLK pins if the USART is configured for synchronous mode.
* Set GPIO mode. */
if (USART0->CTRL & USART_CTRL_SYNC) {
USART0->ROUTE |= USART_ROUTE_CSPEN | USART_ROUTE_CLKPEN;
GPIO_PinModeSet (( GPIO_Port_TypeDef )AF_USART0_TX_PORT(USER_LOCATION), AF_USART0_TX_PIN(USER_LOCATION), gpioModePushPull , 0);
GPIO_PinModeSet (( GPIO_Port_TypeDef )AF_USART0_RX_PORT(USER_LOCATION), AF_USART0_RX_PIN(USER_LOCATION), gpioModeInput , 0);
GPIO_PinModeSet (( GPIO_Port_TypeDef )AF_USART0_CS_PORT(USER_LOCATION), AF_USART0_CS_PIN(USER_LOCATION), gpioModePushPull , 0);
GPIO_PinModeSet (( GPIO_Port_TypeDef )AF_USART0_CLK_PORT(USER_LOCATION), AF_USART0_CLK_PIN(USER_LOCATION), gpioModePushPull , 0);
} else {
/* To avoid false start, configure TX pin as initial high */
GPIO_PinModeSet (( GPIO_Port_TypeDef )AF_USART0_TX_PORT(USER_LOCATION), AF_USART0_TX_PIN(USER_LOCATION), gpioModePushPull , 1);
GPIO_PinModeSet (( GPIO_Port_TypeDef )AF_USART0_RX_PORT(USER_LOCATION), AF_USART0_RX_PIN(USER_LOCATION), gpioModeInput , 0);
/* Don't enable CTS/RTS hardware flow control pins in this example. */
}
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

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_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,