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Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
Interfacing rs232
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Interfacing rs232

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  • 1. Interfacing RS232
  • 2. What is RS232 <ul><li>RS means Recommended Standard. </li></ul><ul><li>RS 232 uses both synchronous and asynchronous communication. </li></ul><ul><li>In microcontrollers like ATmel 89C51 asynchronous communication is used and it is called as UART – universal asynchronous receiver and transmitter </li></ul>
  • 3. Interfacing RS232 <ul><li>We need a driver to use the RS232 with microcontroller </li></ul><ul><li>That driver turned out to be MAX232 </li></ul><ul><li>It is a16 PIN Ic which is used to interface RS232 with any other devices. </li></ul><ul><li>The transmission speed in the RS232 is called as baud rate. </li></ul>
  • 4. Interfacing microcontroller with RS232 standard devices
  • 5. Setting serial port <ul><li>In microcontroller there are some special function registers which are allocated to control the serial communication </li></ul><ul><li>The list of registers which is used to control the serial port are </li></ul><ul><ul><li>SCON </li></ul></ul><ul><ul><li>PCON </li></ul></ul><ul><ul><li>SBUF </li></ul></ul>
  • 6. Double the baud rate <ul><li>The baud rate standards are </li></ul><ul><ul><ul><li>1200 </li></ul></ul></ul><ul><ul><ul><li>2400 </li></ul></ul></ul><ul><ul><ul><li>4800 </li></ul></ul></ul><ul><ul><ul><li>9600 </li></ul></ul></ul><ul><li>But we can manually increase the baud rate into double the normal baud rate by setting the SMOD bit </li></ul><ul><li>SMOD bit is located in PCON register. </li></ul>
  • 7. How to calculate baud rate <ul><li>It is all depend upon the frequency </li></ul><ul><li>Our frequency is 11.0592MHz </li></ul><ul><li>Atmel has 12 Tcycles for a machine cycle </li></ul><ul><li>Every instruction except branch instructions, execute in one machine cycle </li></ul><ul><li>To obtain the speed of operation we have to use the timers again. Unlike the previous classes, timers will be used to generate speed here. </li></ul>
  • 8. Speed calculation <ul><li>11.0592M/12 = 921600 </li></ul><ul><li>921600/32 = 28800  here 32 is the division factor it can be changed to 16 by setting SMOD bit </li></ul><ul><li>28800/?? = speed </li></ul><ul><li>To get required speed we have to choose the value and store it in timer registers </li></ul><ul><li>For example: for 9600 the value is 3. in TH1 it will be FD ie., 256-3=253  FD </li></ul>
  • 9. Normal baud rate and double the normal baud rate <ul><li>SMOD = 0 SMOD = 1 </li></ul><ul><li>1200 2400 </li></ul><ul><li>2400 4800 </li></ul><ul><li>4800 9600 </li></ul><ul><li>9600 19200 </li></ul>
  • 10. Transmit and Receive <ul><li>Every thing is depends upon the interrupt when it comes to microcontroller, it is true that serial communication is not an exceptional for this. </li></ul><ul><li>Transmit interrupt(TI) and receive interrupt(RI) are the two interrupt that control that operation of the serial communication </li></ul>
  • 11. Transmission of data <ul><li>Data can be store in the BUFFER assigned for serial communication(SBUF) </li></ul><ul><li>Transmission will be complete when the transmit buffer is empty </li></ul><ul><li>After acknowledging the transmit interrupt enabled due to empty transmit buffer we can reset the TI and continue the next transmission </li></ul>
  • 12. Example for transmission <ul><li>Consider a letter A is going to be send through serial communication </li></ul><ul><li>Then the coding should be </li></ul><ul><li>SBUF=‘A’; </li></ul><ul><li>While(TI==0); </li></ul><ul><li>TI=0; </li></ul>
  • 13. Receive operation <ul><li>It is reverse of the transmit operation </li></ul><ul><li>The interrupt for the receive will be enabled when the receive buffer is full </li></ul><ul><li>After receiving the acknowledgment of the receive complete the value can be read from BUFFER (SBUF) </li></ul>
  • 14. Example for receive data <ul><li>Consider a ‘A’ is send to microcontroller through the serial port </li></ul><ul><li>The program logic is </li></ul><ul><li>While(RI==0); </li></ul><ul><li>Read=SBUF; </li></ul><ul><li>RI=0; </li></ul>
  • 15. Programming serial <ul><li>It is the same as all the interfacing with microcontroller </li></ul><ul><li>Functions to solve the problem </li></ul><ul><li>Since we not only receive or send a character but a lot of characters. </li></ul><ul><li>Therefore a function will make it easy to get and send all the data we required. </li></ul>
  • 16. Assignments <ul><li>Send your name in serial port </li></ul><ul><li>Get a data from serial port </li></ul><ul><li>Try work with different baud rate </li></ul><ul><li>Get a floating point from serial port and manipulate it and print in LCD(round off the floating point data) </li></ul>

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