ATMEGA323L-4AI View Datasheet(PDF) - Atmel Corporation

Part Name

Description

Manufacturer

ATMEGA323L-4AI

8-bit Microcontroller with 32K Bytes of In-System Programmable Flash

Atmel Corporation 

ATmega323(L)

Receiving Frames with 9 Data

Bits

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

nine bit characters and the status bits.

Assembly Code Example(1)

USART_Receive:

; Wait for data to be received

sbis UCSRA, RXC

rjmp USART_Receive

; Get status and ninth bit, then data from buffer

in r18, UCSRA

in r17, UCSRB

in 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 ninth 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 ninth bit, then data */

/* from buffer */

status = UCSRA;

resh = UCSRB;

resl = UDR;

/* If error, return -1 */

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

return -1;

/* Filter the ninth bit, then return */

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

return ((resh << 8) | resl);

}

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

85

1457G–AVR–09/03

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