Receiver Transmitter (USART)

The Universal Synchronous Asynchronous Receiver Transceiver (USART) provides one full duplex universal synchronous asynchronous serial link. Data frame format is widely programmable (data length, parity, number of stop bits) to support a maximum of standards. The receiver implements parity error, framing error and overrun error detection. The receiver time-out enables handling variable-length frames and the transmitter timeguard facilitates communications with slow remote devices. Multidrop communications are also supported through address bit handling in reception and transmission. The driver supports the following modes: RS232, RS485, SPI, IrDA, ISO7816, MODEM, Hardware handshaking and LIN.

Macros
#define	HIGH_FRQ_SAMPLE_DIV 16

#define	ISO7816_T_0 0

#define	ISO7816_T_1 1

#define	LOW_FRQ_SAMPLE_DIV 8

#define	MAX_CD_VALUE US_BRGR_CD_Msk

#define	MAX_TRAN_GUARD_TIME US_TTGR_TG_Msk

#define	MIN_CD_VALUE 0x01

#define	MIN_CD_VALUE_SPI 0x04

#define	US_WPMR_WPKEY_PASSWD US_WPMR_WPKEY(0x555341U)

#define	USART_PARITY_ERROR 5

Functions
void	usart_disable_interrupt (Usart *p_usart, uint32_t ul_sources)
	Disable USART interrupts. More...

void	usart_disable_rx (Usart *p_usart)
	Disable USART receiver. More...

void	usart_disable_tx (Usart *p_usart)
	Disable USART transmitter. More...

void	usart_disable_writeprotect (Usart *p_usart)
	Disable write protect of USART registers. More...

void	usart_drive_RTS_pin_high (Usart *p_usart)
	Drive the pin RTS to 1. More...

void	usart_drive_RTS_pin_low (Usart *p_usart)
	Drive the pin RTS to 0. More...

void	usart_enable_interrupt (Usart *p_usart, uint32_t ul_sources)
	Enable USART interrupts. More...

void	usart_enable_rx (Usart *p_usart)
	Enable USART receiver. More...

void	usart_enable_tx (Usart *p_usart)
	Enable USART transmitter. More...

void	usart_enable_writeprotect (Usart *p_usart)
	Enable write protect of USART registers. More...

uint32_t	usart_get_interrupt_mask (Usart *p_usart)
	Read USART interrupt mask. More...

uint32_t	usart_get_status (Usart *p_usart)
	Get current status. More...

uint32_t	usart_get_writeprotect_status (Usart *p_usart)
	Get write protect status. More...

uint32_t	usart_getchar (Usart p_usart, uint32_t c)
	Read from USART Receive Holding Register. More...

uint32_t	usart_init_hw_handshaking (Usart p_usart, const sam_usart_opt_t p_usart_opt, uint32_t ul_mck)
	Configure USART to work in hardware handshaking mode. More...

uint32_t	usart_init_rs232 (Usart p_usart, const sam_usart_opt_t p_usart_opt, uint32_t ul_mck)
	Configure USART to work in RS232 mode. More...

uint32_t	usart_init_rs485 (Usart p_usart, const sam_usart_opt_t p_usart_opt, uint32_t ul_mck)
	Configure USART to work in RS485 mode. More...

uint32_t	usart_init_spi_master (Usart p_usart, const usart_spi_opt_t p_usart_opt, uint32_t ul_mck)
	Configure USART to work in SPI mode and act as a master. More...

uint32_t	usart_init_spi_slave (Usart p_usart, const usart_spi_opt_t p_usart_opt)
	Configure USART to work in SPI mode and act as a slave. More...

uint32_t	usart_init_sync_master (Usart p_usart, const sam_usart_opt_t p_usart_opt, uint32_t ul_mck)
	Configure USART to work in SYNC mode and act as a master. More...

uint32_t	usart_init_sync_slave (Usart p_usart, const sam_usart_opt_t p_usart_opt)
	Configure USART to work in SYNC mode and act as a slave. More...

uint32_t	usart_is_rx_ready (Usart *p_usart)
	Check if the received data are ready. More...

uint32_t	usart_is_tx_empty (Usart *p_usart)
	Check if Transmit Holding Register is empty. More...

uint32_t	usart_is_tx_ready (Usart *p_usart)
	Check if Transmit is Ready. More...

uint32_t	usart_putchar (Usart *p_usart, uint32_t c)
	Write to USART Transmit Holding Register. More...

uint32_t	usart_read (Usart p_usart, uint32_t c)
	Read from USART Receive Holding Register. More...

void	usart_reset (Usart *p_usart)
	Reset the USART and disable TX and RX. More...

void	usart_reset_rx (Usart *p_usart)
	Immediately stop and disable USART receiver. More...

void	usart_reset_status (Usart *p_usart)
	Reset status bits (PARE, OVER, MANERR, UNRE and PXBRK in US_CSR). More...

void	usart_reset_tx (Usart *p_usart)
	Immediately stop and disable USART transmitter. More...

void	usart_restart_rx_timeout (Usart *p_usart)
	Restart the receive timeout. More...

uint32_t	usart_send_address (Usart *p_usart, uint32_t ul_addr)
	In Multidrop mode only, the next character written to the US_THR is sent with the address bit set. More...

uint32_t	usart_set_async_baudrate (Usart *p_usart, uint32_t baudrate, uint32_t ul_mck)
	Calculate a clock divider(CD) and a fractional part (FP) for the USART asynchronous modes to generate a baudrate as close as possible to the baudrate set point. More...

void	usart_set_rx_timeout (Usart *p_usart, uint32_t timeout)
	Configure the receive timeout register. More...

static uint32_t	usart_set_spi_master_baudrate (Usart *p_usart, uint32_t baudrate, uint32_t ul_mck)
	Calculate a clock divider (CD) for the USART SPI master mode to generate a baud rate as close as possible to the baud rate set point. More...

static void	usart_set_spi_slave_baudrate (Usart *p_usart)
	Select the SCK pin as the source of baudrate for the USART SPI slave mode. More...

static uint32_t	usart_set_sync_master_baudrate (Usart *p_usart, uint32_t baudrate, uint32_t ul_mck)
	Calculate a clock divider for the USART synchronous master modes to generate a baudrate as close as possible to the baudrate set point. More...

static void	usart_set_sync_slave_baudrate (Usart *p_usart)
	Select the SCK pin as the source of baud rate for the USART synchronous slave modes. More...

void	usart_set_tx_timeguard (Usart *p_usart, uint32_t timeguard)
	Configure the transmit timeguard register. More...

void	usart_spi_force_chip_select (Usart *p_usart)
	Drive the slave select line NSS (RTS pin) to 0 in SPI master mode. More...

void	usart_spi_release_chip_select (Usart *p_usart)
	Drive the slave select line NSS (RTS pin) to 1 in SPI master mode. More...

void	usart_start_rx_timeout (Usart *p_usart)
	Start waiting for a character before clocking the timeout count. More...

void	usart_start_tx_break (Usart *p_usart)
	Start transmission of a break. More...

void	usart_stop_tx_break (Usart *p_usart)
	Stop transmission of a break. More...

uint32_t	usart_write (Usart *p_usart, uint32_t c)
	Write to USART Transmit Holding Register. More...

void	usart_write_line (Usart p_usart, const char string)
	Write one-line string through USART. More...

#define HIGH_FRQ_SAMPLE_DIV 16

Referenced by usart_set_async_baudrate().

#define ISO7816_T_0 0

#define ISO7816_T_1 1

#define LOW_FRQ_SAMPLE_DIV 8

Referenced by usart_set_async_baudrate().

#define MAX_CD_VALUE US_BRGR_CD_Msk

Referenced by usart_set_async_baudrate(), usart_set_spi_master_baudrate(), and usart_set_sync_master_baudrate().

#define MAX_TRAN_GUARD_TIME US_TTGR_TG_Msk

#define MIN_CD_VALUE 0x01

#define MIN_CD_VALUE_SPI 0x04

#define US_WPMR_WPKEY_PASSWD US_WPMR_WPKEY(0x555341U)

Referenced by usart_disable_writeprotect(), and usart_enable_writeprotect().

#define USART_PARITY_ERROR 5

void usart_disable_interrupt	(	Usart *	p_usart,
		uint32_t	ul_sources
	)

Disable USART interrupts.

Parameters

p_usart	Pointer to a USART peripheral.
ul_sources	Interrupt sources bit map.

void usart_disable_rx ( Usart * p_usart )

Disable USART receiver.

Parameters

p_usart Pointer to a USART instance.

void usart_disable_tx ( Usart * p_usart )

Disable USART transmitter.

Parameters

p_usart Pointer to a USART instance.

void usart_disable_writeprotect ( Usart * p_usart )

Disable write protect of USART registers.

Parameters

p_usart Pointer to a USART instance.

References US_WPMR_WPKEY_PASSWD.

Referenced by usart_reset().

void usart_drive_RTS_pin_high ( Usart * p_usart )

Drive the pin RTS to 1.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_reset().

void usart_drive_RTS_pin_low ( Usart * p_usart )

Drive the pin RTS to 0.

Parameters

p_usart Pointer to a USART instance.

void usart_enable_interrupt	(	Usart *	p_usart,
		uint32_t	ul_sources
	)

Enable USART interrupts.

Parameters

p_usart	Pointer to a USART peripheral.
ul_sources	Interrupt sources bit map.

void usart_enable_rx ( Usart * p_usart )

Enable USART receiver.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_serial_init().

void usart_enable_tx ( Usart * p_usart )

Enable USART transmitter.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_serial_init().

void usart_enable_writeprotect ( Usart * p_usart )

Enable write protect of USART registers.

Parameters

p_usart Pointer to a USART instance.

References US_WPMR_WPKEY_PASSWD.

uint32_t usart_get_interrupt_mask ( Usart * p_usart )

Read USART interrupt mask.

Parameters

p_usart Pointer to a USART peripheral.

Returns: The interrupt mask value.

uint32_t usart_get_status ( Usart * p_usart )

Get current status.

Parameters

p_usart Pointer to a USART instance.

Returns: The current USART status.

uint32_t usart_get_writeprotect_status ( Usart * p_usart )

Get write protect status.

Parameters

p_usart Pointer to a USART instance.

Returns: 0 if no write protect violation occurred, or 16-bit write protect violation source.

uint32_t usart_getchar	(	Usart *	p_usart,
		uint32_t *	c
	)

Read from USART Receive Holding Register.

Before reading user should check if rx is ready.

Parameters

p_usart	Pointer to a USART instance.
c	Pointer where the one-byte received data will be stored.

Return values

0	Data has been received.
1	on failure.

uint32_t usart_init_hw_handshaking	(	Usart *	p_usart,
		const sam_usart_opt_t *	p_usart_opt,
		uint32_t	ul_mck
	)

Configure USART to work in hardware handshaking mode.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.
ul_mck	USART module input clock frequency.

Return values

0	on success.
1	on failure.

References usart_init_rs232().

uint32_t usart_init_rs232	(	Usart *	p_usart,
		const sam_usart_opt_t *	p_usart_opt,
		uint32_t	ul_mck
	)

Configure USART to work in RS232 mode.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.
ul_mck	USART module input clock frequency.

Return values

0	on success.
1	on failure.

References sam_usart_opt_t::baudrate, sam_usart_opt_t::channel_mode, sam_usart_opt_t::char_length, sam_usart_opt_t::parity_type, sam_usart_opt_t::stop_bits, usart_reset(), and usart_set_async_baudrate().

Referenced by usart_init_hw_handshaking(), usart_init_rs485(), and usart_serial_init().

uint32_t usart_init_rs485	(	Usart *	p_usart,
		const sam_usart_opt_t *	p_usart_opt,
		uint32_t	ul_mck
	)

Configure USART to work in RS485 mode.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.
ul_mck	USART module input clock frequency.

Return values

0	on success.
1	on failure.

References usart_init_rs232().

uint32_t usart_init_spi_master	(	Usart *	p_usart,
		const usart_spi_opt_t *	p_usart_opt,
		uint32_t	ul_mck
	)

Configure USART to work in SPI mode and act as a master.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.
ul_mck	USART module input clock frequency.

Return values

0	on success.
1	on failure.

References usart_spi_opt_t::baudrate, usart_spi_opt_t::channel_mode, usart_spi_opt_t::char_length, usart_spi_opt_t::spi_mode, SPI_MODE_0, SPI_MODE_1, SPI_MODE_2, SPI_MODE_3, usart_reset(), and usart_set_spi_master_baudrate().

uint32_t usart_init_spi_slave	(	Usart *	p_usart,
		const usart_spi_opt_t *	p_usart_opt
	)

Configure USART to work in SPI mode and act as a slave.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.

Return values

0	on success.
1	on failure.

References usart_spi_opt_t::channel_mode, usart_spi_opt_t::char_length, usart_spi_opt_t::spi_mode, SPI_MODE_0, SPI_MODE_1, SPI_MODE_2, SPI_MODE_3, usart_reset(), and usart_set_spi_slave_baudrate().

uint32_t usart_init_sync_master	(	Usart *	p_usart,
		const sam_usart_opt_t *	p_usart_opt,
		uint32_t	ul_mck
	)

Configure USART to work in SYNC mode and act as a master.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.
ul_mck	USART module input clock frequency.

Return values

0	on success.
1	on failure.

References sam_usart_opt_t::baudrate, sam_usart_opt_t::channel_mode, sam_usart_opt_t::char_length, sam_usart_opt_t::parity_type, sam_usart_opt_t::stop_bits, usart_reset(), and usart_set_sync_master_baudrate().

uint32_t usart_init_sync_slave	(	Usart *	p_usart,
		const sam_usart_opt_t *	p_usart_opt
	)

Configure USART to work in SYNC mode and act as a slave.

Note: By default, the transmitter and receiver aren't enabled.

Parameters

p_usart	Pointer to a USART instance.
p_usart_opt	Pointer to sam_usart_opt_t instance.

Return values

0	on success.
1	on failure.

References sam_usart_opt_t::channel_mode, sam_usart_opt_t::char_length, sam_usart_opt_t::parity_type, sam_usart_opt_t::stop_bits, usart_reset(), and usart_set_sync_slave_baudrate().

uint32_t usart_is_rx_ready ( Usart * p_usart )

Check if the received data are ready.

Check if Data have been received and loaded into USART_RHR.

Parameters

p_usart Pointer to a USART instance.

Return values

1	Some data has been received.
0	No data has been received.

Referenced by usart_serial_is_rx_ready().

uint32_t usart_is_tx_empty ( Usart * p_usart )

Check if Transmit Holding Register is empty.

Check if the last data written in USART_THR have been loaded in TSR and the last data loaded in TSR have been transmitted.

Parameters

p_usart Pointer to a USART instance.

Return values

1	Transmitter is empty.
0	Transmitter is not empty.

uint32_t usart_is_tx_ready ( Usart * p_usart )

Check if Transmit is Ready.

Check if data have been loaded in USART_THR and are waiting to be loaded into the Transmit Shift Register (TSR).

Parameters

p_usart Pointer to a USART instance.

Return values

1	No data is in the Transmit Holding Register.
0	There is data in the Transmit Holding Register.

uint32_t usart_putchar	(	Usart *	p_usart,
		uint32_t	c
	)

Write to USART Transmit Holding Register.

Note: Before writing user should check if tx is ready (or empty).

Parameters

p_usart	Pointer to a USART instance.
c	Data to be sent.

Return values

0	on success.
1	on failure.

Referenced by usart_write_line().

uint32_t usart_read	(	Usart *	p_usart,
		uint32_t *	c
	)

Read from USART Receive Holding Register.

Note: Before reading user should check if rx is ready.

Parameters

p_usart	Pointer to a USART instance.
c	Pointer where the one-byte received data will be stored.

Return values

0	on success.
1	if no data is available or errors.

Referenced by usart_serial_getchar().

void usart_reset ( Usart * p_usart )

Reset the USART and disable TX and RX.

Parameters

p_usart Pointer to a USART instance.

References usart_disable_writeprotect(), usart_drive_DTR_pin_high(), usart_drive_RTS_pin_high(), usart_reset_rx(), usart_reset_status(), and usart_reset_tx().

Referenced by usart_init_rs232(), usart_init_spi_master(), usart_init_spi_slave(), usart_init_sync_master(), and usart_init_sync_slave().

void usart_reset_rx ( Usart * p_usart )

Immediately stop and disable USART receiver.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_reset().

void usart_reset_status ( Usart * p_usart )

Reset status bits (PARE, OVER, MANERR, UNRE and PXBRK in US_CSR).

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_reset().

void usart_reset_tx ( Usart * p_usart )

Immediately stop and disable USART transmitter.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_reset().

void usart_restart_rx_timeout ( Usart * p_usart )

Restart the receive timeout.

Parameters

p_usart Pointer to a USART instance.

uint32_t usart_send_address	(	Usart *	p_usart,
		uint32_t	ul_addr
	)

In Multidrop mode only, the next character written to the US_THR is sent with the address bit set.

Parameters

p_usart	Pointer to a USART instance.
ul_addr	The address to be sent out.

Return values

0	on success.
1	on failure.

References usart_write().

uint32_t usart_set_async_baudrate	(	Usart *	p_usart,
		uint32_t	baudrate,
		uint32_t	ul_mck
	)

Calculate a clock divider(CD) and a fractional part (FP) for the USART asynchronous modes to generate a baudrate as close as possible to the baudrate set point.

Note: Baud rate calculation: Baudrate = ul_mck/(Over * (CD + FP/8)) (Over being 16 or 8). The maximal oversampling is selected if it allows to generate a baudrate close to the set point.

Parameters

p_usart	Pointer to a USART instance.
baudrate	Baud rate set point.
ul_mck	USART module input clock frequency.

Return values

0	Baud rate is successfully initialized.
1	Baud rate set point is out of range for the given input clock frequency.

References HIGH_FRQ_SAMPLE_DIV, LOW_FRQ_SAMPLE_DIV, and MAX_CD_VALUE.

Referenced by usart_init_rs232().

void usart_set_rx_timeout	(	Usart *	p_usart,
		uint32_t	timeout
	)

Configure the receive timeout register.

Parameters

p_usart	Pointer to a USART instance.
timeout	The value of receive timeout.

static uint32_t usart_set_spi_master_baudrate	(	Usart *	p_usart,
		uint32_t	baudrate,
		uint32_t	ul_mck
	)

static

Calculate a clock divider (CD) for the USART SPI master mode to generate a baud rate as close as possible to the baud rate set point.

Note: Baud rate calculation: \( Baudrate = \frac{SelectedClock}{CD} \).

Parameters

p_usart	Pointer to a USART instance.
baudrate	Baud rate set point.
ul_mck	USART module input clock frequency.

Return values

0	Baud rate is successfully initialized.
1	Baud rate set point is out of range for the given input clock frequency.

References MAX_CD_VALUE.

Referenced by usart_init_spi_master().

static void usart_set_spi_slave_baudrate ( Usart * p_usart )

static

Select the SCK pin as the source of baudrate for the USART SPI slave mode.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_init_spi_slave().

static uint32_t usart_set_sync_master_baudrate	(	Usart *	p_usart,
		uint32_t	baudrate,
		uint32_t	ul_mck
	)

static

Calculate a clock divider for the USART synchronous master modes to generate a baudrate as close as possible to the baudrate set point.

Note: Synchronous baudrate calculation: baudrate = ul_mck / cd

Parameters

p_usart	Pointer to a USART instance.
baudrate	Baud rate set point.
ul_mck	USART module input clock frequency.

Return values

0	Baud rate is successfully initialized.
1	Baud rate set point is out of range for the given input clock frequency.

References MAX_CD_VALUE.

Referenced by usart_init_sync_master().

static void usart_set_sync_slave_baudrate ( Usart * p_usart )

static

Select the SCK pin as the source of baud rate for the USART synchronous slave modes.

Parameters

p_usart Pointer to a USART instance.

Referenced by usart_init_sync_slave().

void usart_set_tx_timeguard	(	Usart *	p_usart,
		uint32_t	timeguard
	)

Configure the transmit timeguard register.

Parameters

p_usart	Pointer to a USART instance.
timeguard	The value of transmit timeguard.

void usart_spi_force_chip_select ( Usart * p_usart )

Drive the slave select line NSS (RTS pin) to 0 in SPI master mode.

Parameters

p_usart Pointer to a USART instance.

void usart_spi_release_chip_select ( Usart * p_usart )

Drive the slave select line NSS (RTS pin) to 1 in SPI master mode.

Parameters

p_usart Pointer to a USART instance.

void usart_start_rx_timeout ( Usart * p_usart )

Start waiting for a character before clocking the timeout count.

Reset the status bit TIMEOUT in US_CSR.

Parameters

p_usart Pointer to a USART instance.

void usart_start_tx_break ( Usart * p_usart )

Start transmission of a break.

Parameters

p_usart Pointer to a USART instance.

void usart_stop_tx_break ( Usart * p_usart )

Stop transmission of a break.

Parameters

p_usart Pointer to a USART instance.

uint32_t usart_write	(	Usart *	p_usart,
		uint32_t	c
	)

Write to USART Transmit Holding Register.

Note: Before writing user should check if tx is ready (or empty).

Parameters

p_usart	Pointer to a USART instance.
c	Data to be sent.

Return values

0	on success.
1	on failure.

Referenced by usart_send_address(), usart_serial_putchar(), and usart_write_char_buf().

void usart_write_line	(	Usart *	p_usart,
		const char *	string
	)

Write one-line string through USART.

Parameters

p_usart	Pointer to a USART instance.
string	Pointer to one-line string to be sent.

References usart_putchar().

Microchip® Advanced Software Framework

Macros

Functions