atmega323l ATMEL Corporation, atmega323l Datasheet - Page 85

• Manufacturer Part Number: atmega323l
• Description: Atmega323 8-bit Avr Microcontroller With 32k Bytes Of In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Receiving Frames with 9 Data
Bits
1457G–AVR–09/03
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.
Note:
Assembly Code Example
C Code Example
USART_Receive:
USART_ReceiveNoError:
unsigned int USART_Receive( void )
{
}
; Wait for data to be received
sbis UCSRA, RXC
rjmp USART_Receive
; Get status and ninth bit, then data from buffer
in
in
in
; If error, return -1
andi r18,(1<<FE)|(1<<DOR)|(1<<PE)
breq USART_ReceiveNoError
ldi
ldi
; Filter the ninth bit, then return
lsr
andi r17, 0x01
ret
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) )
/* Filter the ninth bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
1. The example code assumes that the part specific header file is included.
return -1;
r18, UCSRA
r17, UCSRB
r16, UDR
r17, HIGH(-1)
r16, LOW(-1)
r17
(1)
(1)
ATmega323(L)
85