Datasheet

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 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 */
if ( status & (1<<FE)|(1<<DOR)|(1<<PE) )
return -1;
/* Filter the 9th bit, then return */
resh = (resh >> 1) & 0x01;
return ((resh << 8) | resl);
}
Note: 1. See About Code Examples.
The receive function example reads all the I/O Registers into the Register File before any
computation is done. This gives an optimal receive buffer utilization since the buffer
location read will be free to accept new data as early as possible.
Related Links
About Code Examples
24.7.3 Receive Compete Flag and Interrupt
The USART Receiver has one flag that indicates the Receiver state.
The Receive Complete (RXC) Flag indicates if there are unread data present in the receive buffer. This
flag is one when unread data exist in the receive buffer, and zero when the receive buffer is empty (i.e.,
does not contain any unread data). If the Receiver is disabled (RXEN = 0), the receive buffer will be
flushed and consequently the RXC bit will become zero.
When the Receive Complete Interrupt Enable (RXCIE) in UCSRB is set, the USART Receive Complete
Interrupt will be executed as long as the RXC Flag is set (provided that global interrupts are enabled).
When interrupt-driven data reception is used, the receive complete routine must read the received data
from UDR in order to clear the RXC Flag, otherwise a new interrupt will occur once the interrupt routine
terminates.
24.7.4 Receiver Error Flags
The USART Receiver has three error flags: Frame Error (FE), Data OverRun (DOR) and Parity Error
(PE). All can be accessed by reading UCSRA. Common for the error flags is that they are located in the
receive buffer together with the frame for which they indicate the error status. Due to the buffering of the
error flags, the UCSRA must be read before the receive buffer (UDR), since reading the UDR I/O location
AVR 8-Bit Microcontroller
USART - Universal Synchronous and Asynchrono...
© 2017 Microchip Technology Inc.
Datasheet Complete
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