ATmega16 datasheet(148/315 Pages) ATMEL

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148

ATmega16(L)

2466E–AVR–10/02

Receiving Frames with 9

Databits

If 9 bit characters are used (UCSZ=7) the ninth bit must be read from the RXB8 bit in

UCSRB before reading the low bits from the UDR. This rule applies to the FE, DOR and

PE status flags as well. Read status from UCSRA, then data from UDR. Reading the

UDR I/O location will change the state of the receive buffer FIFO and consequently the

TXB8, FE, DOR and PE bits, which all are stored in the FIFO, will change.

The following code example shows a simple USART receive function that handles both

9-bit characters and the status bits.

Note:

1. The example code assumes that the part specific header file is included.

Assembly Code Example(1)

USART_Receive:

; Wait for data to be received

sbis

UCSRA, RXC

rjmp

USART_Receive

; Get status and 9th bit, then data from buffer

r18, UCSRA

r17, UCSRB

r16, UDR

; If error, return -1

andi

r18,(1<<FE)|(1<<DOR)|(1<<PE)

breq

USART_ReceiveNoError

ldi

r17, HIGH(-1)

ldi

r16, LOW(-1)

USART_ReceiveNoError:

; Filter the 9th bit, then return

lsr

r17

andi

r17, 0x01

ret

C Code Example

(1)

unsigned int

USART_Receive( void )

{

unsigned char

status, resh, resl;

/* Wait for data to be received */

while

( !(UCSRA & (1<<RXC)) )

;

/* Get status and 9th bit, then data */

/* from buffer */

status = UCSRA;

resh = UCSRB;

resl = UDR;

/* If error, return -1 */

( status & (1<<FE)|(1<<DOR)|(1<<PE) )

return

-1;

/* Filter the 9th bit, then return */

resh = (resh >> 1) & 0x01;

return

((resh << 8) | resl);

}

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