AT90PWM2 datasheet(197/365 Pages) ATMEL

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197

AT90PWM2/3

4317B–AVR–02/05

Parity bit. Can be odd or even.

Stop bit, always high.

IDLE

No transfers on the communication line (RxD or TxD). An IDLE line must be

high.

The frame format used by the USART is set by the UCSZ2:0, UPM1:0 and USBS bits in

UCSRB and UCSRC. The Receiver and Transmitter use the same setting. Note that

changing the setting of any of these bits will corrupt all ongoing communication for both

the Receiver and Transmitter.

The USART Character SiZe (UCSZ2:0) bits select the number of data bits in the frame.

The USART Parity mode (UPM1:0) bits enable and set the type of parity bit. The selec-

tion between one or two stop bits is done by the USART Stop Bit Select (USBS) bit. The

Receiver ignores the second stop bit. An FE (Frame Error) will therefore only be

detected in the cases where the first stop bit is zero.

Parity Bit Calculation

The parity bit is calculated by doing an exclusive-or of all the data bits. If odd parity is

used, the result of the exclusive or is inverted. The relation between the parity bit and

data bits is as follows:

even

Parity bit using even parity

Podd

Parity bit using odd parity

Data bit n of the character

If used, the parity bit is located between the last data bit and first stop bit of a serial

frame.

USART Initialization

The USART has to be initialized before any communication can take place.

The configuration between the USART or EUSART mode should be done before any

other configuration.

The initialization process normally consists of setting the baud rate, setting frame format

and enabling the Transmitter or the Receiver depending on the usage.

For interrupt driven USART operation, the Global Interrupt Flag should be cleared (and

interrupts globally disabled) when doing the initialization.

Before doing a re-initialization with changed baud rate or frame format, be sure that

there are no ongoing transmissions during the period the registers are changed. The

TXC flag can be used to check that the Transmitter has completed all transfers, and the

RXC flag can be used to check that there are no unread data in the receive buffer. Note

that the TXC flag must be cleared before each transmission (before UDR is written) if it

is used for this purpose.

even

–

… d

odd

⊕

⊕⊕

–

… d

⊕

⊕⊕

AT90PWM2 Datasheet(PDF) 197 Page - ATMEL Corporation

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