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Programming 8051 SPORT (Assembly Language)

Programming 8051 SPORT (Assembly Language). serial communication. The data is sent one bit at a time. serial communication uses single data line making it much cheaper. serial communication. 2 methods, asynchronous and synchronous

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Programming 8051 SPORT (Assembly Language)

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  1. Programming8051 SPORT(Assembly Language)

  2. serial communication • The data is sent one bit at a time. • serial communication uses single data line making it much cheaper.

  3. serial communication • 2 methods, asynchronous and synchronous • synchronous method transfers a block of data (characters) at a time • asynchronous method transfers a single byte at a time • Uses special IC chips called UART (universal asynchronous receiver-transmitter) and USART (universal synchronous­asynchronous receiver-transmitter) • 8051 chip has a built-in UART

  4. Simple and Duplex transmission

  5. Simple and Duplex transmission • Half- and full-duplex transmission • simplex (one way) communication allows data to be transmitted in only one direction • duplex(two way) communication allows data to be transmitted in two directions. • duplex transmissions can be half or full duplex • If one way at a time, it is half duplex • If can go both ways at the same time, it is full duplex • full duplex requires two wire conductors for the data lines (in addition to the signal ground)

  6. Asynchronous serial communication and data framing • data coming in 0s and 1s • to make sense of the data sender and receiver agree on a set of rules • Protocol determines • how the data is packed • how many bits/character • when the data begins and ends

  7. Asynchronous serial communication and data framing cont… • Start and stop bits • asynchronous method, each character is placed between start and stop bits • called framing • start bit is always one bit • stop bit can be one or two bits • start bit is always a 0 (low) • stop bit(s) is 1 (high) • LSB is sent out first

  8. Framing ASCII “A” When there is no data transfer the signal is highTransmission begins with a start (low) bitLSB firstFinally 1 stop bit (high)Data transfer rate (baud rate) is stated in bps

  9. Baud rate • Data transfer rate • rate of data transfer is stated in bps (bits per second) • widely used terminology for bps is baud rate • baud and bps rates are not necessarily equal • The baud rate is the number of times per second a serial communication signal changes states; a state being either a voltage level, a frequency, or a frequency phase angle.

  10. RS232 Standard • This standard is used in PCs • Logic 1 : -3 to -25 volt • Logic 0 : 3 to 25 volt • To Connect TXD to RXD and RXD to TXD from pc to 8051 you must use max232 to convert signal from TTL level to RS232 level • The baud rate of the 8051 must matched the baud rate of the pc • PC standard baud rate (see hyper terminal configuration) • 2400-4800-9600-14400-19200-28800-33600-57600

  11. 8051 Serial Port • 8051 has an internal UART • P3.0 (pin 11) is assigned to TxD • P3.1 (pin 10) is assigned to Rxd • Baud rate is set by Timer1 • these pins are TTL compatible • require a line driver to make them RS232 compatible • driver is the MAX232 chip • SBUF : Serial Buffer Register • There are physically two SBUF registers having same address i.e 99 H. • Data moved to SBUF is Transmitted serially • Serial data Rx-ed is stored by CPU in SBUF

  12. SM0 SM1 SM2 REN TB8 RB8 TI RI Serial control (SCON) Register 7 6 5 4 3 2 1 0 SM2: used for multi processor communication (Make it 0) REN: receive enable (by software enable/disable) TB8: Not widely used RB8: Not widely used TI: transmit interrupt flag set by HW after send , clear by SW RI: receive interrupt flag set by HW after received ,clear by SW SM0 SM1 MODE operation transmit rate 0 0 0 shift register fixed (xtal/12) 0 1 1 8 bit UART variable (timer1) 1 0 2 9 bit UART fixed (xtal/32 or xtal/64) 1 1 3 9 bit UART variable (timer1) SM0: mode specifier SM1: mode specifier

  13. Mode of operation • Mode 1 • Ten bits are transmitted (through TxD) or received (through RxD) (A start bit (0), 8 data bits (LSB first), and a stop bit (1) ) • On receive, the stop bit goes into RB8 in SCON • the baud rate is determined by the Timer 1 overflow rate (not by TF1). • Timer1 clock is (1/32) machine cycle (MC=1/12 XTAL) To timer1 to set baudrate

  14. Finding timer1 registers values 11.0592MHz Xtal frequency allows the 8051 system to communicate with the PC without any error. Machine cycle frequency = 11.0592 MHz/ 12 = 921.6 kHz Timer1 clock = 921.6 kHz / 32 = 28,800 Hz Initial value in TH1 = 256 – (Timer1 clock / Required baudrate) Example: For 9600 baud rate TH1 = 256 – ( 28800/9600) = 256 – 3 = 253 = FDh or -3 For 2400 baud rate TH1 = 256 – ( 28800/2400) = 256 – 12 = 253 = F4h or -12

  15. Doubling Baud Rate • Ways of Increasing the baud rate • increase the crystal frequency • set SMOD bit in the PCON register (baud rate will doubled) PCON Register (SFR address 87) How to set SMOD Mov a, pcon Setb acc.7 Mov pcon, a

  16. Doubling baud ratecont...

  17. Programming the 8051 to transfer data serially • Load TMOD with value 20h. Timer1 mode 2 ( 8bit auto reload ) • Load calculated initial value into TH1 register • Write 40h into SCON (mode 1, REN =0) • Start timer by SETB TR1 • Clear TI by CLR TI • Write data to be transmitted into SBUF • Keep monitoring TI using the instruction JNB TI, xx TI is set while transmitting the Stop bit • Go to step 5 to transfer the next byte

  18. Program for sending data( in mode 1 ) Transfer letter ‘A’ serially at 9600 baudrate org 0 ljmp main org 030h main: MOV TMOD,#20H ;TIMER 1 MODE 2 MOV TH1,#-3 ;9600 BAUD MOV TL1,#-3 ;9600 BAUD MOV SCON,#40H ;mode 1, REN = 0 SETB TR1 ;start timer1 again: CLR TI ; Clear TI to transfer the next ; character MOV SBUF, #”‘A”;SBUF = 41H • wait: JNB TI, wait ; wait for the last bit • SJMP again ; keep sending A • end

  19. Programming the 8051 to receive data serially • Load TMOD with value 20h. Timer1 mode 2 ( 8bit auto reload ) • Load calculated initial value into TH1 register • Write 50h into SCON (mode 1, REN = 1) • Start timer by SETB TR1 • Keep monitoring RI using the instruction JNB RI, xx • RI is set while receiving the Stop bit • Save received data • Clear RI get ready to receive next byte • Go to step 5 to receive next byte

  20. Program for receiving data( in mode 1 ) Receive serial data with 9600 baud rate, 1 start bit, 1 stop bit and 8 data bit and write it into port 1 org 0 ljmpmain org 030h main: MOV TMOD,#20H ;Timer1 mode 2 MOV TH1,#-3 ;9600 baud rate MOV SCON,#50H ;mode 1 & Rx Enable SETB TR1 ;start timer1 • WAIT: JNB RI, WAIT ;wait for char to come in • MOV A,SBUF ; save incoming byte in A • MOV P1, A ; send to port 1 • CLR RI ; get ready to receive next byte • SJMP WAIT ; keep getting data • end

  21. Thank you

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