Техническая Спецификация для Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI
Модели
MEGA328P-XMINI
179
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
Notes: 1.
These transmit functions are written to be general functions. They can be optimized if the contents of the
UCSRnB is static. For example, only the TXB8 bit of the UCSRnB Register is used after initialization.
UCSRnB is static. For example, only the TXB8 bit of the UCSRnB Register is used after initialization.
2.
The ninth bit can be used for indicating an address frame when using multi processor communication mode or
for other protocol handling as for example synchronization.
for other protocol handling as for example synchronization.
20.6.3 Transmitter Flags and Interrupts
The USART Transmitter has two flags that indicate its state: USART Data Register Empty (UDREn) and
Transmit Complete (TXCn). Both flags can be used for generating interrupts.
Transmit Complete (TXCn). Both flags can be used for generating interrupts.
The Data Register Empty (UDREn) Flag indicates whether the transmit buffer is ready to receive new data. This
bit is set when the transmit buffer is empty, and cleared when the transmit buffer contains data to be transmitted
that has not yet been moved into the Shift Register. For compatibility with future devices, always write this bit to
zero when writing the UCSRnA Register.
bit is set when the transmit buffer is empty, and cleared when the transmit buffer contains data to be transmitted
that has not yet been moved into the Shift Register. For compatibility with future devices, always write this bit to
zero when writing the UCSRnA Register.
When the Data Register Empty Interrupt Enable (UDRIEn) bit in UCSRnB is written to one, the USART Data
Register Empty Interrupt will be executed as long as UDREn is set (provided that global interrupts are enabled).
UDREn is cleared by writing UDRn. When interrupt-driven data transmission is used, the Data Register Empty
interrupt routine must either write new data to UDRn in order to clear UDREn or disable the Data Register
Empty interrupt, otherwise a new interrupt will occur once the interrupt routine terminates.
Register Empty Interrupt will be executed as long as UDREn is set (provided that global interrupts are enabled).
UDREn is cleared by writing UDRn. When interrupt-driven data transmission is used, the Data Register Empty
interrupt routine must either write new data to UDRn in order to clear UDREn or disable the Data Register
Empty interrupt, otherwise a new interrupt will occur once the interrupt routine terminates.
The Transmit Complete (TXCn) Flag bit is set one when the entire frame in the Transmit Shift Register has been
shifted out and there are no new data currently present in the transmit buffer. The TXCn Flag bit is automatically
cleared when a transmit complete interrupt is executed, or it can be cleared by writing a one to its bit location.
The TXCn Flag is useful in half-duplex communication interfaces (like the RS-485 standard), where a
shifted out and there are no new data currently present in the transmit buffer. The TXCn Flag bit is automatically
cleared when a transmit complete interrupt is executed, or it can be cleared by writing a one to its bit location.
The TXCn Flag is useful in half-duplex communication interfaces (like the RS-485 standard), where a
Assembly Code Example
USART_Transmit:
; Wait for empty transmit buffer
in r16, UCSRnA
sbrs r16, UDREn
rjmp
USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi
UCSRnB,TXB8
sbrc
r17,0
sbi
UCSRnB,TXB8
; Put LSB data (r16) into buffer, sends the data
out
UDRn,r16
ret
C Code Example
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRnA & (1<<UDREn))) )
;
/* Copy 9th bit to TXB8 */
UCSRnB &= ~(1<<TXB8);
if ( data & 0x0100 )
UCSRnB |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDRn = data;
}