interfacing AVR with SERIAL PORT OF COMPUTER
This tutorial is taken from the book MY EXPERIENCE IN PROGRAMMING AVR MICROCONTROLLER IN C USING WINAVR/AVRGCC. you can download it free from the files section(FILE-AVRBOOK.RAR) of yahoo group-booksbybibin http://groups.yahoo.com/group/booksbybibin/ comments about this book on www.booksbybibin.blogspot.com SERIAL PORT OF COMPUTER BIOS SETTINGS FOR SERIAL PORT First set the bios then only do any other operations like programming the microcontroller and serial port. See the Port numbers correctly. Then only use the COM1, COM2 or lpt1,lpt2 repectively. This is the most important step. AVRDUDE programmer sometimes won't work for some parallel port. It does not worked for INTEL965GV motherboard. So see my previous book on parallel port before doing these steps. SERIAL PORT INTERFACING WITH COMPUTER For interfacing AVR with serial port of cable you require a serial port cable and max232 or HIN232(level converter). RS-232 of the computer has LOGIC HIGH in the range of -3 to -25V( mostly around -8.5V) and LOGIC LOW around 3 to 25V (mostly 8.5V). We had to convert it to LOGIC HIGH(5V) and LOGIC LOW(0V) of microcontroller, so we use max232 or you can use any other level converters. Next is to get a serial port cable,if you are not getting a serial port cable, then buy a serial mouse costs around Rs.70 and take the cable from it. But mouse serial port cable has only 4 pins Rx,Tx,DTS,GND, so it can't be used for programmer's of some microcontrollers. But in our case we require only 3 pins(Rx,Tx,GND). So it is better to go for a serial cable, I used one that of mouse. Figure shows the connections with serial port of computer. You can use a 1uF capacitor instead of 10uF. HYPER TERMINAL Hyper Terminal is used to see the serial port data. It will show only the received data. All the data is show in ASCII. Go to Start_Programs_Accessories_Communicatin_Hyper Terminal. If you are using serial port for your internet you have to disconnect it for acessing serial port. Run Hyper Terminal then some screen come for asking area codes, put some garbage value and press OK and in the next page press OK, then you will come to this page. If you use some USB to RS232 converter, then I can't say that Hyper Terminal will work or not. It does not worked for me. See in the device manager for the port settings. Device Manage COM Properties device manager Testing your computer Serial Port: Short circuit Rx and Tx of your computer and type letters keeping hyperterminal working. If you can see what you are typing(i.e, if you type 'a' then it is displayed as 'a' on the hyperterminal) then you can infer that your serial port will work properly. Don't use ground and other pins,leave all other pins open and just short circuit pin2 and pin3(Rx and Tx). serial5 Now connect serial port to max232, then short circuit the Rx and Tx of max232 ie pin 11 and pin 12 and type something in hyperterminal, see what you are getting. If you are getting the alphabets you typed then your connections are proper. Max232 is working fine. By default the TTL output is 5V. See the RS232 output corresponding to 5V input, it should be mostly in the range -8V to -10V. See these conditions properly otherwise your microcontroller will get burned because voltage greater than 5V is damagerous to the microcontroller. FOLDER:serial_computer(see avrbook.rar from yahoo group-booksbybibin) /*this program sends back the next ascii value u typed*/ /*---------------------------------------------------------------- -----------------HEADER FILES------------------------------------- -----------------------------------------------------------------*/ #include <avr/io.h> /*---------------------------------------------------------------- -----------------FUNCTIONS--------------------------------------- -----------------------------------------------------------------*/ void InitUART( unsigned char baudrate ); unsigned char ReceiveByte( void ); void TransmitByte( unsigned char data ); /*---------------------------------------------------------------- -----------------MAIN FUNCTION------------------------------------ -----------------------------------------------------------------*/ void main() { InitUART( 25 ); /* Set the baudrate to 2400 bps using a 1MHz crystal */ for(;;) /* Forever */ { TransmitByte(ReceiveByte()+1); /* Echo the received character */ } } /*---------------------------------------------------------------- ------------FUNCTIONS TO Initialize UART-------------------------- -----------------------------------------------------------------*/ void InitUART( unsigned char baudrate ) { UBRRL = baudrate; /* Set the baud rate */ UCSRB = (UCSRB | _BV(RXEN) | _BV(TXEN) ); /* Enable UART receiver and transmitter */ } /*---------------------------------------------------------------- ------------FUNCTIONS TO READ UART------------------------------- -----------------------------------------------------------------*/ unsigned char ReceiveByte( void ) { while ( !(UCSRA & (_BV(RXC))) ); /* Wait for incomming data */ return UDR;/* Return the data */ } /*---------------------------------------------------------------- ------------FUNCTIONS TO WRITE UART------------------------------- -----------------------------------------------------------------*/ void TransmitByte( unsigned char data ) { while ( !(UCSRA & (_BV(UDRE))) ); /* Wait for empty transmit buffer */ UDR = data; /* Start transmittion */ } Here this code will send back next ASCII you type. See the error in baud rates for different clock frequencies. Here I am using 2400 8 N 1 with 1Mhz internal crystal. If you want more speed then go for internal 8Mhz crystal. But still error is around .2%, so if you want 0% error in baud rate go for crystal 3.6864Mhz or crystals given in the datasheet which is having 0% error in baud rate TransmitByte(ReceiveByte()+1); You can use terminal program inbuilt in WinXP or Bray's terminal for serial port interfacing with computer. Bray's terminal is a free software with more options than hyperterminal. Hyperterminal won't show the transmitted data, it shows only the received data. SERIAL PORT TROUBLESHOOTING AND ERRORS: When synchronisation is lost you will get xxxxxxxxxxxxxxxxx displayed on hyperterminal. So be thorough about the micrcontroller clock and baud rate you set. This is the most important error occurs with serial port. If you use a C program then you will get some different values other than the values you sent. Remember only one program can acess serial port at a time. Sometimes Turbo C is having problem in acessing serial ports. I am attaching a C program with it.