AT90PWM2 datasheet(222/365 Pages) ATMEL

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222

AT90PWM2/3

4317B–AVR–02/05

The EUSART is actived with the EUSART bit of EUCSRB register. Until this bit is not

set, the USART will behave as standard USART, all the functionnalities of the EUSART

are not accessible.

The EUSART supports more serial frame formats than the standard USART interface:

•

Asynchonous frames

–

Standard bit level encoded

–

Manchester bit encoded

•

Synchronous frames

–

In this mode only the Standard bit level encoded is available

Serial Frames

A serial frame is defined to be one character of data bits with synchronization bits (start

and stop bits), and optionally a parity bit for error checking.

Frame Formats

The EUSART allows to receive and transmit serial frame with the following format:

•

1 start bit

•

5, 6, 7, 8, 9, 13, 14,15,16,17 data bits

•

data bits and start bit level encoded or Manchester encoded

•

data transmition MSB or LSB first (bit ordering)

•

no, even or odd parity bit

•

1 or 2 stop bits:

–

Stop bits insertion for transmition

–

Stop bits value read access in reception

The frame format used by the EUSART can be configured through the following

USART/EUSART registers:

•

UTxS3:0 and URxS3:0 (EUCSRA of EUSART register) select the number of data

bits per frame

•

UPM1:0 bits enable and set the type of parity bit (when configured in Manchester

mode, the parity should be fixed to none).

USBS (UCSRC register of USART) and EUSBS (EUCSRB register of EUSART) select

the number of stop bits to be processed respectively by the transmiter and the receiver.

The receiver stores the two stop bit values when configured in Manchester mode. When

configured in level encoded mode, the second stop bit is ignored (behavior similar as

the USART).

Parity Bit Calculation

The parity bit behavior is similar to the USART mode, except for the Manchester

encoded mode, where no parity bit can be inserted or detected (should be configured to

none with the UPM1:0 bits. 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

odd

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.

even

–

… d

odd

⊕

⊕⊕

–

… d

⊕

⊕⊕

AT90PWM2 Datasheet(PDF) 222 Page - ATMEL Corporation

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