Rainbow-electronics Atmega169L Manuel d'utilisateur télécharger pdf (Page 158)

158

ATmega169V/L

2514A–AVR–08/02

Sending Frames with 9 Data

Bit

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

UCSRB before the low byte of the character is written to UDR. 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.

Notes: 1. These transmit functions are written to be general functions. They can be optimized if

the contents of the UCSRB is static. For example, only the TXB8 bit of the UCSRB

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

For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”,

and “SBI” instructions must be replaced with instructions that allow access to

extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and

“CBR”.

The ninth bit can be used for indicating an address frame when using multi processor

communication mode or for other protocol handling as for example synchronization.

Assembly Code Example

(1)(2)

USART_Transmit:

;

Wait for empty transmit buffer

sbis UCSRA,UDRE

rjmp USART_Transmit

;

Copy 9th bit from r17 to TXB8

cbi UCSRB,TXB8

sbrc r17,0

sbi UCSRB,TXB8

;

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

out UDR,r16

ret

C Code Example

(1)(2)

void USART_Transmit( unsigned int data )

{

Wait for empty transmit buffer

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

;

Copy 9th bit to TXB8

UCSRB &= ~(1<<TXB8);

if ( data & 0x0100 )

UCSRB |= (1<<TXB8);

Put data into buffer, sends the data

UDR = data;

}

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