UA EN RU
GreenChip.com.ua

Опубликовано 2010-05-07 11:30:31 автором Ruslan

Data transfer via the UART AVR. Lesson 9 AVR


Microcontroller to communicate with his older brother - the PC - you can use the data interfaces , but since I'm training on AVR I try to build on the microcontroller mega8 , it is preferable to communicate with all PC use interface USART . No, you can certainly zayuzat USB, but USART in mega8 implemented in hardware , which means that we do not have to manually implement logic data , we simply write the data into the register , but the process itself is already sending steer MK hardware .
Protocol UART (Universal asynchronous receiver / transmitter) is one of the most common protocols for data transfer between devices. At one Atmega8 USART, he launched on legs PD0 - Rx, receiver ( receiver) and PD1 - Tx, transmitter ( transmitter) .

Vyvod Usart have mega8 Let's try to transfer data from your PC. When the PC will come with a 1, then the LED will glow when 0, then fade . The layout is as follows: Uart have proteus Next we need to write a program in:
CodeVision AVR create a new project , the frequency u set at 8 megahertz , then go to the tab USART, there include the transmitter and receiver

Uart have proteus Remove all unnecessary and its code 's update 

 # include <mega8.h>  
 void main (void)  
 { 
 char date = 0 ;  
   PORTC = 0x00;  
 DDRC = 0x01;    
 / / USART initialization  
 / / Communication Parameters: 8 Data, 1 Stop, No Parity  
 / / USART Receiver: On  
 / / USART Transmitter: On  
 / / USART Mode: Asynchronous  
 / / USART Baud Rate: 9600  
 UCSRA = 0x00;  
 UCSRB = 0x18;  
 UCSRC = 0x86;  
 UBRRH = 0x00;  
 UBRRL = 0x33;  
   while ( 1 )  
 { 
 date = UDR;  
  
 if (date == '1 ') PORTC.0 = 1 ;  
 if (date == '0 ') PORTC.0 = 0 ;  
 } ;  
 }

Do AVR have register UDR . In fact , these are two different registers , which have one address . When the write data, then they get to the register of the transmitter , and when we read - taken from the receive register . To send , we just write the data into the register and they will fly to the receiver , and if something came to us - we read them from the register .
Follow UART no need to turn all the service you can hang on interruption. When we come to the data , an interrupt is generated on completion of reception, and when the data will go - will be caused devastation interrupt
Compile program throws in microns in Proteus . To send data from the terminal should tick near: peredacha data through uart Input "1" - LED lights

uart in Proteus

Enter "0" - LED goes

peredacha data via uart in Proteus

Job interrupt

As you have noticed , our program infinitely waits for bytes. Impractical to do so because the main loop loaded sending and receiving data via uart and nothing else can not do. Of course , you can not get hung up , and periodically for example every 10 milliseconds to check if we have not come data for the rest of their time doing something . But then, if the channel is set at high speed , you can skip bytes . Best of all this stir raspberries interrupt : the data came - volunteered to interrupt handler and all . For this CodeWizard AVR USART tab should tick near Rx Interrapt

uart on preryvaniyah
generates code and get 

 # include <mega8.h>  
 # ifndef RXB8  
 # define RXB8 1  
 # endif    
 # ifndef TXB8  
 # define TXB8 0  
 # endif    
 # ifndef UPE  
 # define UPE 2  
 # endif    
 # ifndef DOR  
 # define DOR 3  
 # endif    
 # ifndef FE  
 # define FE 4  
 # endif    
 # ifndef UDRE  
 # define UDRE 5  
 # endif    
 # ifndef RXC  
 # define RXC 7  
 # endif    
 # define FRAMING_ERROR ( 1 < < FE)  
 # define PARITY_ERROR ( 1 < < UPE)  
 # define DATA_OVERRUN ( 1 < < DOR)  
 # define DATA_REGISTER_EMPTY ( 1 < < UDRE)  
 # define RX_COMPLETE ( 1 < < RXC)    
             // USART Receiver buffer  
 # define RX_BUFFER_SIZE 8   char rx_buffer [RX_BUFFER_SIZE];    
 # if RX_BUFFER_SIZE < 256   unsigned char rx_wr_index, rx_rd_index, rx_counter;  
 # else   unsigned int rx_wr_index, rx_rd_index, rx_counter;  
 # endif
     // This flag is set on USART Receiver buffer overflow   bit rx_buffer_overflow;    
 // USART Receiver interrupt service routine   interrupt [USART_RXC] void usart_rx_isr (void)  
 {  char status, data;   status = UCSRA;  
 data = UDR;  
 if ((status & (FRAMING_ERROR | PARITY_ERROR | DATA_OVERRUN)) == 0 )  
 { 
 rx_buffer [rx_wr_index] = data;  
 if (+ + rx_wr_index == RX_BUFFER_SIZE) rx_wr_index = 0 ;  
 if (+ + rx_counter == RX_BUFFER_SIZE)  
 { 
 rx_counter = 0 ;  
 rx_buffer_overflow = 1 ;  
 };  
 };  
 if (data == '1 ') PORTC.0 = 1 ;  
 if (data == '0 ') PORTC.0 = 0 ;  
 }  
  
 # include <stdio.h>    
 void main (void)  
 { 
 / / Port C initialization  
 PORTC = 0x00;  
 DDRC = 0x01;    
 // USART initialization  
 // Communication Parameters: 8 Data, 1 Stop, No Parity  
 // USART Receiver: On  
 // USART Transmitter: Off  
 // USART Mode: Asynchronous  
 // USART Baud Rate: 9600  
 UCSRA = 0x00;  
 UCSRB = 0x90;  
 UCSRC = 0x86;  
 UBRRH = 0x00;  
 UBRRL = 0x33;  
   / / Global enable interrupts  
 # asm ("sei")  
   while ( 1 )  
 { 
 };  
 }

Here codewizard generated different parity, and a buffer for the data records that came from. Us to light the LED this is not necessary , so remove unnecessary and get 

 # include <mega8.h>  
 # include < stdio.h >   
 / / USART Receiver interrupt service routine   interrupt [USART_RXC] void usart_rx_isr (void)  
 { 
 char data;  
 data = UDR;  
  
 if (data == '1 ') PORTC.0 = 1 ;  
 if (data == '0 ') PORTC.0 = 0 ;  
 }  
  
 void main (void)  
 { 
 // Port C initialization  
 PORTC = 0x00;  
 DDRC = 0x01;  
   // USART initialization  
 // Communication Parameters: 8 Data, 1 Stop, No Parity  
 // USART Receiver: On  
 // USART Transmitter: Off  
 // USART Mode: Asynchronous  
 // USART Baud Rate: 9600  
 UCSRA = 0x00;  
 UCSRB = 0x90;  
 UCSRC = 0x86;  
 UBRRH = 0x00;  
 UBRRL = 0x33;  
   // Global enable interrupts  
 # asm ("sei")  
  
 while ( 1)
   { 
 };  
 }

As you can see , the main loop is free. Now we do not need to be checked regularly , and do not come any data on uart. When will byte uart, then the interrupt handler is invoked , and we will make it necessary for us action .

Proceed to iron
If your PC has COM port you to interface with the microcontroller will need a level converter TTL - RS232. It is easy to assemble on-chip MAX232. It is needed because the output voltage data from COM- port of the PC :
  • logical " 1 " from -5 to -15
  • volt logic " 0 " from +5 to +15 V
and u
  • logical " 1 " from 1,8 to voltage V
  • logical \ " 0 \" from 0 to 1,3 V
Wiring RS232 is about the Shema RS232 connection about takaya If your PC has no COM ports , you need juzat adapter chip FT232 - it connects to USB your PC and appears in the system virtual COM port , and on the findings of the appropriate signals FT232 UART. Shema RS232 connection about takaya

Комментарии - (2)

Добавить комментарий

Для отправки комментария вы должны авторизоваться.