Техническая Спецификация для Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI
Модели
MEGA328P-XMINI
199
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
21.5.1 USART MSPIM Initialization
The USART in MSPIM mode has to be initialized before any communication can take place. The initialization
process normally consists of setting the baud rate, setting master mode of operation (by setting DDR_XCKn to
one), setting frame format and enabling the Transmitter and the Receiver. Only the transmitter can operate
independently. For interrupt driven USART operation, the Global Interrupt Flag should be cleared (and thus
interrupts globally disabled) when doing the initialization.
process normally consists of setting the baud rate, setting master mode of operation (by setting DDR_XCKn to
one), setting frame format and enabling the Transmitter and the Receiver. Only the transmitter can operate
independently. For interrupt driven USART operation, the Global Interrupt Flag should be cleared (and thus
interrupts globally disabled) when doing the initialization.
Note:
To ensure immediate initialization of the XCKn output the baud-rate register (UBRRn) must be zero at the time the
transmitter is enabled. Contrary to the normal mode USART operation the UBRRn must then be written to the
desired value after the transmitter is enabled, but before the first transmission is started. Setting UBRRn to zero
before enabling the transmitter is not necessary if the initialization is done immediately after a reset since UBRRn is
reset to zero.
transmitter is enabled. Contrary to the normal mode USART operation the UBRRn must then be written to the
desired value after the transmitter is enabled, but before the first transmission is started. Setting UBRRn to zero
before enabling the transmitter is not necessary if the initialization is done immediately after a reset since UBRRn is
reset to zero.
Before doing a re-initialization with changed baud rate, data mode, or frame format, be sure that there is no
ongoing transmissions during the period the registers are changed. The TXCn Flag can be used to check that
the Transmitter has completed all transfers, and the RXCn Flag can be used to check that there are no unread
data in the receive buffer. Note that the TXCn Flag must be cleared before each transmission (before UDRn is
written) if it is used for this purpose.
ongoing transmissions during the period the registers are changed. The TXCn Flag can be used to check that
the Transmitter has completed all transfers, and the RXCn Flag can be used to check that there are no unread
data in the receive buffer. Note that the TXCn Flag must be cleared before each transmission (before UDRn is
written) if it is used for this purpose.
The following simple USART initialization code examples show one assembly and one C function that are equal
in functionality. The examples assume polling (no interrupts enabled). The baud rate is given as a function
parameter. For the assembly code, the baud rate parameter is assumed to be stored in the r17:r16 registers.
in functionality. The examples assume polling (no interrupts enabled). The baud rate is given as a function
parameter. For the assembly code, the baud rate parameter is assumed to be stored in the r17:r16 registers.