AT90SCR100 datasheet(238/433 Pages) ATMEL

238 / 433 page

238

TPR0327AY–SMS–30Jan09

AT90SCR100

18.7

Data Transmission – The USART Transmitter

The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSR0B

den by the USART and given the function as the Transmitter’s serial output. The baud rate,

mode of operation and frame format must be set up once before doing any transmissions. If syn-

chronous operation is used, the clock on the XCK pin will be overridden and used as

transmission clock.

18.7.1

Sending Frames with 5 to 8 Data Bit

A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The

CPU can load the transmit buffer by writing to the UDR0 I/O location. The buffered data in the

transmit buffer will be moved to the Shift Register when the Shift Register is ready to send a new

frame. The Shift Register is loaded with new data if it is in idle state (no ongoing transmission) or

immediately after the last stop bit of the previous frame is transmitted. When the Shift Register is

loaded with new data, it will transfer one complete frame at the rate given by the Baud Register,

U2X0 bit or by XCK depending on mode of operation.

The following code examples show a simple USART transmit function based on polling of the

Data Register Empty

(UDRE0) Flag. When using frames with less than eight bits, the most sig-

nificant bits written to the UDR0 are ignored. The USART has to be initialized before the function

can be used. For the assembly code, the data to be sent is assumed to be stored in Register

R16

Note:

1. See “About Code Examples” on page 11.

The function simply waits for the transmit buffer to be empty by checking the UDRE0 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.

Assembly Code Example(1)

USART_Transmit:

; Wait for empty transmit buffer

sbis

UCSR0A,UDRE0

rjmp

USART_Transmit

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

out

UDR0,r16

ret

C Code Example (1)

void

USART_Transmit( unsigned char data )

{

/* Wait for empty transmit buffer */

while

( !( UCSR0A & (1<<UDRE0)) )

;

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

UDR0 = data;

}

AT90SCR100 Datasheet(PDF) 238 Page - ATMEL Corporation

AT90SCR100 Datasheet(HTML) 238 Page - ATMEL Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL