ATmega16 datasheet(163/357 Pages) ATMEL

163 / 357 page

163

2466S–AVR–05/09

ATmega16(L)

The following code example shows how to read the UCSRC Register contents.

Note:

1. See “About Code Examples” on page 7.

The assembly code example returns the UCSRC value in r16.

Reading the UBRRH contents is not an atomic operation and therefore it can be read as an ordi-

nary register, as long as the previous instruction did not access the register location.

USART Register

Description

USART I/O Data

The USART Transmit Data Buffer Register and USART Receive Data Buffer Registers share the

same I/O address referred to as USART Data Register or UDR. The Transmit Data Buffer Reg-

ister (TXB) will be the destination for data written to the UDR Register location. Reading the

UDR Register location will return the contents of the Receive Data Buffer Register (RXB).

For 5-, 6-, or 7-bit characters the upper unused bits will be ignored by the Transmitter and set to

zero by the Receiver.

The transmit buffer can only be written when the UDRE Flag in the UCSRA Register is set. Data

written to UDR when the UDRE Flag is not set, will be ignored by the USART Transmitter. When

data is written to the transmit buffer, and the Transmitter is enabled, the Transmitter will load the

data into the transmit Shift Register when the Shift Register is empty. Then the data will be seri-

ally transmitted on the TxD pin.

The receive buffer consists of a two level FIFO. The FIFO will change its state whenever the

receive buffer is accessed. Due to this behavior of the receive buffer, do not use read modify

write instructions (SBI and CBI) on this location. Be careful when using bit test instructions (SBIC

and SBIS), since these also will change the state of the FIFO.

Assembly Code Example

(1)

USART_ReadUCSRC:

; Read UCSRC

r16,UBRRH

r16,UCSRC

ret

C Code Example(1)

unsigned char

USART_ReadUCSRC( void )

{

unsigned char

ucsrc;

/* Read UCSRC */

ucsrc = UBRRH;

ucsrc = UCSRC;

return ucsrc;

}

Bit

RXB[7:0]

UDR (Read)

TXB[7:0]

UDR (Write)

Read/Write

R/W

Initial Value

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