A000003 Arduino, A000003 Datasheet - Page 178
A000003
Manufacturer Part Number
A000003
Description
MCU, MPU & DSP Development Tools MINI
Manufacturer
Arduino
Series
-r
Type
MCUr
Specifications of A000003
Processor To Be Evaluated
Atmega328
Processor Series
ATmega
Data Bus Width
8 bit
Interface Type
USB, RS-232
Operating Supply Voltage
7 V to 9 V
Contents
Board
Lead Free Status / Rohs Status
Lead free / RoHS Compliant
For Use With/related Products
ATmega168
- Current page: 178 of 378
- Download datasheet (8Mb)
19.6
19.6.1
178
Data Transmission – The USART Transmitter
ATmega48/88/168
Sending Frames with 5 to 8 Data Bit
The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSRnB
Register. When the Transmitter is enabled, the normal port operation of the TxDn pin is overrid-
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 XCKn pin will be overridden and used as
transmission clock.
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 UDRn 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,
U2Xn bit or by XCKn depending on mode of operation.
The following code examples show a simple USART transmit function based on polling of the
Data Register Empty (UDREn) Flag. When using frames with less than eight bits, the most sig-
nificant bits written to the UDRn 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:
Assembly Code Example
C Code Example
USART_Transmit:
void USART_Transmit( unsigned char data )
{
}
; Wait for empty transmit buffer
sbis UCSRnA,UDREn
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out
ret
/* Wait for empty transmit buffer */
while ( !( UCSRnA & (1<<UDREn)) )
/* Put data into buffer, sends the data */
UDRn = data;
1.
See ”About Code Examples” on page 7.
UDRn,r16
;
(1)
(1)
2545S–AVR–07/10
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