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          EEPW首頁 > 嵌入式系統(tǒng) > 設(shè)計(jì)應(yīng)用 > 用于ATmega128的軟件UART范例程序

          用于ATmega128的軟件UART范例程序

          作者: 時(shí)間:2012-10-29 來源:網(wǎng)絡(luò) 收藏

          一般教科書上提供的收發(fā)的往往是一段采用輪循(Polling)方式完成收發(fā)的簡單代碼。但對于高速的AVR來講,采用這種方式大大降低了 MUC的效率。在使用AVR時(shí),應(yīng)根據(jù)芯片本身的特點(diǎn)(片內(nèi)大容量數(shù)據(jù)存儲(chǔ)器RAM,更適合采用高級(jí)語言編寫系統(tǒng)),編寫高效可靠的收發(fā)接口(低層)。下面是一個(gè)典型的USART的接口程序。

          本文引用地址:http://www.ex-cimer.com/article/170727.htm

          #include

          #define RXB8 1

          #define TXB8 0

          #define UPE 2

          #define OVR 3

          #define FE 4

          #define UDRE 5

          #define RXC 7

          #define FRAMING_ERROR (1

          #define PARITY_ERROR (1

          #define DATA_OVERRUN (1

          #define DATA_REGISTER_EMPTY (1

          #define RX_COMPLEte (1

          // USART0 Receiver buffer

          #define RX_BUFFER_SIZE0 8

          char rx_buffer0[RX_BUFFER_SIZE0];

          unsigned char rx_wr_index0,rx_rd_index0,rx_counter0;

          // This flag is set ON USART0 Receiver buffer overflow

          bit rx_buffer_overflow0;

          // USART0 Receiver interrupt service routine

          #pragma savereg-

          interrupt [USART0_RXC] void uart0_rx_isr(void)

          {

          char status,data;

          #asm

          push r26

          push r27

          push r30

          push r31

          in r26,sreg

          push r26

          #endasm

          status=UCSR0A;

          data=UDR0;

          if ((status (FRAMING_ERROR | PARITY_ERROR | DATA_OVERRUN))==0)

          {

          rx_buffer0[rx_wr_index0]=data;

          if (++rx_wr_index0 == RX_BUFFER_SIZE0) rx_wr_index0=0;

          if (++rx_counter0 == RX_BUFFER_SIZE0)

          {

          rx_counter0=0;

          rx_buffer_overflow0=1;

          };

          };

          #asm

          pop r26

          out sreg,r26

          pop r31

          pop r30

          pop r27

          pop r26

          #endasm

          }

          #pragma savereg+

          #ifndef _DEBUG_TERMINAL_IO_

          // Get a character from the USART0 Receiver buffer

          #define _ALTERNATE_GETCHAR_

          #pragma used+

          char getchar(void)

          {

          char data;

          while (rx_counter0==0);

          data=rx_buffer0[rx_rd_index0];

          if (++rx_rd_index0 == RX_BUFFER_SIZE0) rx_rd_index0=0;

          #asm(cli)

          --rx_counter0;

          #asm(sei)

          return data;

          }

          #pragma used-

          #endif

          // USART0 Transmitter buffer

          #define TX_BUFFER_SIZE0 8

          char tx_buffer0[TX_BUFFER_SIZE0];

          unsigned char tx_wr_index0,tx_rd_index0,tx_counter0;

          // USART0 Transmitter interrupt service routine

          #pragma savereg-

          interrupt [USART0_TXC] void uart0_tx_isr(void)

          {

          #asm

          push r26

          push r27

          push r30

          push r31

          in r26,sreg

          push r26

          #edasm

          if (tx_counter0)

          {

          --tx_counter0;

          UDR0=tx_buffer0[tx_rd_index0];

          if (++tx_rd_index0 == TX_BUFFER_SIZE0) tx_rd_index0=0;

          };

          #asm

          pop r26

          out sreg,r26

          pop r31

          pop r30

          pop r27

          pop r26

          #endasm

          }

          #pragma savereg+

          #ifndef _DEBUG_TERMINAL_IO_

          // Write a character to the USART0 Transmitter buffer

          #define _ALTERNATE_PUTCHAR_

          #pragma used+

          void putchar(char c)

          {

          while (tx_counter0 == TX_BUFFER_SIZE0);

          #asm(cli)

          if (tx_counter0 || ((UCSR0A DATA_REGISTER_EMPTY)==0))

          {

          tx_buffer0[tx_wr_index0]=c;

          if (++tx_wr_index0 == TX_BUFFER_SIZE0) tx_wr_index0=0;

          ++tx_counter0;

          }

          else

          UDR0=c;

          #asm(sei)

          }

          #pragma used-

          #endif

          // Standard Input/Output functions

          #include

          // Declare your global variables here

          void main(void)

          {

          // USART0 initialization

          // Communication Parameters: 8 Data, 1 Stop, No Parity

          // USART0 Receiver: On

          // USART0 Transmitter: On

          // USART0 Mode: Asynchronous

          // USART0 Baud rate: 9600

          UCSR0A=0x00;

          UCSR0B=0xD8;

          UCSR0C=0x06;

          UBRR0H=0x00;

          UBRR0L=0x67;

          // Global enable interrupts

          #asm(sei)

          while (1)

          {

          // Place your code here

          };

          }


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