AT90PWM2 datasheet(212/361 Pages) ATMEL

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4317J–AVR–08/10

AT90PWM2/3/2B/3B

The frame format used by the EUSART can be configured th rough the fo llowing

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 num-

ber 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).

19.3.2

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.

19.3.3

Manchester encoding

Manchester encoding (also know as Biphase Code) is a synchronous clock encoding technique

used to encode the clock and data of a synchronous bit stream. In this technique, the actual

binary data to be transmitted are not sent as a sequence of logic 1's and 0's as in level encoded

way as in standard USART (known technically as Non Return to Zero (NRZ)). Instead, the bits

are translated into a slightly different format that has a number of advantages over using straight

binary encoding (i.e. NRZ).

Manchester encoding follows the rules:

•

If the original data is a Logic 1, the Manchester code is: 0 to 1 (upward transition at bit

center)

•

If the original data is a Logic 0, the Manchester code is: 1 to 0 (downward transition at bit

center)

Figure 19-2. Manchester Bi-phase levels

Peven

dn 1

–

…

Podd

⊕

⊕⊕⊕⊕⊕

dn 1

–

…

⊕

⊕⊕⊕⊕⊕

Logical 0

Logical 1

AT90PWM2 Datasheet(PDF) 212 Page - ATMEL Corporation

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