Serial.ppt and it contains all information
- 1. 1 The 8051 Microcontroller and Embedded Systems Chapter 10 8051 Serial Communications From the text by Mazidi & Mazidi (2000)
- 4. 4 Serial Transfers A protocol is a set of rules agreed by both the sender and receiver on How the data is packed How many bits constitute a character When the data begins and ends Asynchronous serial data communication is widely used for character-oriented transmissions Each character is placed in between start and stop bits, this is called framing Block-oriented data transfers use the synchronous method The start bit is always one bit, but the stop bit can be one or two bits
- 5. 5 Asynchronous • Bit timing is important since both transmitter and receiver need to be in agreement of timing. • Bit Width = 1/Baud rate or bit rate • 9600 Baud = bit width of 104uS
- 6. 6 Setting Baud Rate • For Baud rate, OSC/12 then /32. • Timer 1 in Mode 2 is used as Baud Rate Generator. • 28,800/3 = 9600 baud • 28,800/12 = 2400 baud • 28,800/24 = 1200 baud • And so on.
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- 8. 8 SBUF • Serial buffer, SBUF is used to hold data to be transmitted on TxD, and holds received data on RxD. • Note that there are actually 2 SBUFs, but one is read only and one is write only. MOV SBUF, A MOV A, SBUF
- 9. 9 SCON • SCON, serial control register, is used for serial control. Mode 0: In this mode the serial port function as half duplex serial port with fixed baud rate.
- 10. 10 • REN (receive enable) SCON is a bit-addressable register When REN is high, it allows 8051 to receive data on RxD pin; If low the receiver is disable • TI (transmit interrupt) When 8051 finishes the transfer of 8-bit character It raises TI flag to indicate that it is ready to transfer another byte TI bit is raised at the beginning of the stop bit
- 11. 11 • RI (receive interrupt) When 8051 receives data serially via RxD, it gets rid of the start and stop bits and places the byte in SBUF register It raises the RI flag bit to indicate that a byte has been received and should be picked up before it is lost RI is raised halfway through the stop bit
- 12. 12 Programming the 8051 to transfer serially a. Initialize the timer 1 in mode 2 to perform auto reload. b. Set the baud c. Load SCON with 50H, indicating serial mode1 where 8 bits data are transmit with one start and one stop bit d. Set TR1 to start timer e. clear interrupt flag, CLR, TI f. Character byte to be transfer serially is being written into SBUF g. TI flag is monitored with the use of JNB TI, XX h. To transfer the next character, go to step e
- 13. 13 Programming the 8051 to receive data serially a. Initialize the timer 1 in mode 2 to perform auto reload. b. Set the baud c. Load SCON with 50H, indicating serial mode1 where 8 bits data are transmit with one start and one stop bit d. Set TR1 to start timer e. clear interrupt flag, CLR, RI f. Character byte to be transfer serially is being written into SBUF g. TI flag is monitored with the use of JNB RI, XX h. To transfer the next character, go to step e
- 14. 14 Output? MOV TMOD,#20H ;timer 1,mode 2(auto reload) MOV TH1,#-6 ;4800 baud rate MOV SCON,#50H ;8-bit, 1 stop, REN enabled SETB TR1 ;start timer 1 AGAIN: MOV SBUF,#”A” ;letter “A” to transfer HERE: JNB TI,HERE ;wait for the last bit CLR TI ;clear TI for next char SJMP AGAIN ;keep sending A
- 15. 15 Problems 1. Write a program to transfer the letter ‘y’ serially at 9600 baud connected to P3.1 continuously. 2. Write program to take data through ports P0, P1, and P2 one after another and transfer the data serially one by one. 3. Write the program to receive the data which has been send in serial form and send it out to port 0 in parallel form. Save the data at RAM location 60H 4. Write the program to transfer the numbers 1 to 9 serially. 5. Discuss how baud in 8051 can be doubled?
- 16. 16 Problem 1 MOV TMOD, #20H MOV TH1, #-3 MOV SCON, #50H SETB TR1 CLR TI AGAIN:MOV SBUF, #‘Y’ HERE: JNB TI, HERE CLR TI SJMP AGAIN
- 17. 17 Problem 2 MOV TMOD, #20H MOV TH1, #-3 MOV SCON, #50H MOV P0,#0FFH ; MAKE P0 input port MOV P0,#0FFH MOV P0,#0FFH SETB TR1 CLR TI AGAIN: MOV A, P0 ACALL SEND MOV A, P1 ACALL SEND MOV A, P2 ACALL SEND SJMP AGAIN SEND: MOV SBUF, A HERE: JNB TI, HERE CLR TI RET
- 18. 18 DOUBLING THE BAUDS RATE There are two ways to increase the baud rate of data transfer To use a higher frequency crystal To change a bit in the PCON register PCON register is an 8-bit register When 8051 is powered up, SMOD is zero We can set it to high by software and thereby double the baud rate
- 19. 19 Baud rates for SMOD=0 Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz and 921.6 kHz / 32 = 28,800 Hz since SMOD = 0
- 20. 20 Baud rates for SMOD=1 Machine cycle freq. = 11.0592 MHz / 12 = 921.6 kHz and 921.6 kHz / 16 = 57,600 Hz since SMOD = 1 MOV A, PCON SETB ACC.7 MOV PCON, A