AT90LS4433-4AI datasheet(59/126 Pages) ATMEL

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AT90S/LS4433

1042H–AVR–04/03

• Bit 3 – TXEN: Transmitter Enable

This bit enables the UART Transmitter when set (one). When disabling the Transmitter

while transmitting a character, the Transmitter is not disabled before the character in the

Shift Register plus any following character in UDR has been completely transmitted.

• Bit 2 – CHR9: 9-bit Characters

When this bit is set (one), transmitted and received characters are nine bits long, plus

start and stop bits. The ninth bit is read and written by using the RXB8 and TXB8 bits in

UCSRB, respectively. The ninth data bit can be used as an extra stop bit or a parity bit.

• Bit 1 – RXB8: Receive Data Bit 8

When CHR9 is set (one), RXB8 is the ninth data bit of the received character.

• Bit 0 – TXB8: Transmit Data Bit 8

When CHR9 is set (one), TXB8 is the ninth data bit in the character to be transmitted.

Baud Rate Generator

The Baud Rate Generator is a frequency divider, which generates baud rates according

to the following equation:

•

BAUD = Baud Rate

•f

CK= Crystal Clock frequency

•

UBR = Contents of the UBRRHI and UBRR Registers, (0 - 4095)

For standard crystal frequencies, the most commonly used baud rates can be generated

by using the UBR settings in Table 19. UBR values that yield an actual baud rate differ-

ing less than 2% from the target baud rate are boldface in the table. However, using

baud rates that have more than 1% error is not recommended. High error ratings give

less noise resistance.

BAUD

fCK

16(UBR 1

)

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