Datasheet

ManualsBrandsMICROCHIP TECHNOLOGY ManualsMicrocontrollers, Microprocessors & QuartzesEmbedded microcontroller VFQFN 28 (4x4) 8-Bit 20 MHz I/O number 23

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The function simply waits for the transmit buffer to be empty by checking the UDRE flag, before loading it

with new data to be transmitted. If the data register empty interrupt is utilized, the interrupt routine writes

the data into the buffer.

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9. About Code Examples

24.7.2 Sending Frames with 9 Data Bits

If 9-bit characters are used (UCSZn = 7), the ninth bit must be written to the TXB8 bit in UCSRnB before

the low byte of the character is written to UDRn.

The ninth bit can be used for indicating an address frame when using Multiprocessor Communication

mode or for another protocol handling as for example synchronization.

The following code examples show a transmit function that handles 9-bit characters. For the assembly

code, the data to be sent is assumed to be stored in registers R17:R16.

Assembly Code Example

USART_Transmit:

; Wait for empty transmit buffer

in r18, UCSR0A

sbrs r18, UDRE

rjmp USART_Transmit

; Copy 9th bit from r17 to TXB8

cbi UCSR0B,TXB8

sbrc r17,0

sbi UCSR0B,TXB8

; Put LSB data (r16) into buffer, sends the data

out UDR0,r16

ret

C Code Example

void USART_Transmit( unsigned int data )

{

/* Wait for empty transmit buffer */

while ( !( UCSR0A & (1<<UDRE))) )

;

/* Copy 9th bit to TXB8 */

UCSR0B &= ~(1<<TXB8);

if ( data & 0x0100 )

UCSR0B |= (1<<TXB8);

/* Put data into buffer, sends the data */

UDR0 = data;

}

Note: These transmit functions are written to be general functions. They can be optimized if the contents

of the UCSRnB is static. For example, only the TXB8 bit of the UCSRnB register is used after

initialization.