Instructor: Nachiket M. Kharalkar Lecture 17 Date: 07/16/2007 E-mail: knachike@ece.utexas.edu

1. Introduction to Microcontrollers Instructor: Nachiket M. Kharalkar Lecture 17 Date: 07/16/2007 E-mail: knachike@ece.utexas.edu

2. Today’s Agenda • Output compare interrupt • DAC • Lab 6 discussion • Multiple Access Circular Queues • First in first out queue Nachiket M. Kharalkar

3. Implementation of OC Nachiket M. Kharalkar

4. Typical OC handler ;interrupts every 1000 TCNT cycles ;every 1ms TC0handler lddTC0 addd #1000 stdTC0;setp time for next interrupt movb #$01,TFLG1;acknowledge, clear C0F rti Nachiket M. Kharalkar

5. Resistor network for DAC 1.5 kΩ 1.5 kΩ + 1.5 kΩ 12 kΩ || 12 kΩ 12 kΩ Nachiket M. Kharalkar

6. Dynamic testing Nachiket M. Kharalkar

7. 4-bit sine table SinTab fcb 8,9,11,12,13,14,14,15,15,15,14 fcb 14,13,12,11,9,8,7,5,4,3,2 fcb 2,1,1,1,2,2,3,4,5,7 Nachiket M. Kharalkar

8. 440Hz sine wave output Nachiket M. Kharalkar

9. Data flow graph Nachiket M. Kharalkar

10. Lab 6 demo Nachiket M. Kharalkar

11. Standard music notes Nachiket M. Kharalkar

12. Extra credit • At least 2 output compare interrupts • Play a song • Worth +20 maximum for this lab Nachiket M. Kharalkar

13. Lab 6 Extra credit demo Nachiket M. Kharalkar

14. Multiple Access Circular Queues • Used for data flow problems source to sink • Digital filters and digital controllers • Fixed length • Order preserving • MACQ is always full Nachiket M. Kharalkar

15. Source process (producer) • places information into the MACQ • oldest data is discarded when new data isentered • Sink process (consumer) • can read any data • MACQ is not changed by the read operation. Nachiket M. Kharalkar

16. A multiple access circular queue stores the most recent set of measurements Nachiket M. Kharalkar

17. Perform a 60Hz notch filter on a measured signal • v[0] v[1] v[2] and v[3] are the most recent data sampled at 360 Hz. • filtered output = Nachiket M. Kharalkar

18. 60Hz filter implementation Nachiket M. Kharalkar

19. First in first out queue and double buffers FIFO queues and double buffers can be used to pass data from a producer to a consumer Nachiket M. Kharalkar

20. Producer-consumer examples Nachiket M. Kharalkar

21. A data flow graph showing two FIFO’s that buffer data between producers and consumers Nachiket M. Kharalkar

22. The FIFO implementation with infinite memory Nachiket M. Kharalkar

23. Program 11.1. Code fragments showing the basic idea of a FIFO * Reg A is data to put into the FIFO RxFifo_Put ldx RxPutPt staa 1,X+ store into FIFO stx RxPutPt update pointer rts * Reg A returned with byte from FIFO RxFifo_Get ldx RxGetPt ldaa 1,X+ read from FIFO stx RxGetPt update rts Nachiket M. Kharalkar

24. Three modifications that are required to these functions • If FIFO full when RxFifo_Put is called then the subroutine should return a full error. • If the FIFO is empty when RxFifo_Get is called, then the subroutine should return an empty error. • A finite number of bytes will be permanently allocated Nachiket M. Kharalkar

25. The FIFO Put operation showing the pointer wrap Nachiket M. Kharalkar

26. The FIFO Get operation showing the pointer wrap Nachiket M. Kharalkar

27. RXFIFO_SIZE equ 10 RxPutPt rmb 2 RxGetPt rmb 2 RxFifo rmb RXFIFO_SIZE Program 11.2. Global structures for a two-pointer FIFO. RxFifo_Init ldx #RxFifo stx RxPutPt stx RxGetPt rts Program 11.3. Initialize both pointers to the beginning of the FIFO. Nachiket M. Kharalkar

28. Flowcharts of the put and get operations Nachiket M. Kharalkar

29. Serial Communications Interface ( SCI) • The total number of bits transmitted per second is called the baud rate. • M, selects 8-bit (M=0) or 9-bit (M=1) data frames. • A frame is the smallest complete unit of serial transmission. • The information rate, or bandwidth, is defined as the amount of data or usual information transmitted per second. A serial data frame with M=0 Nachiket M. Kharalkar

30. 6812 SCI Details 9S12C32 SCI ports. Nachiket M. Kharalkar

31. SCIBD & SCIDRL • SCIBD • on 9S12C32 MCLK = 24MHz (with PLL) = 4 MHz (otherwise) • SCI baud rate = __MCLK__ (16*BR) • TE is the Transmitter Enable bit, and • RE is the Receiver Enable bit. • SCIDRL register contains transmit and receive data • these two registers exist at the same I/O port address • Reads access the read-only receive data register (RDR) • Writes access the write-only transmit data register (TDR) Nachiket M. Kharalkar

32. TDRE & RDRF • TDRE is the Transmit Data Register Empty flag. • set by the SCI hardware if transmit data register empty • if set, the software write next output to SCIDRL • cleared by two-step software sequence • first reading SCISR1 with TDRE set • then SCIDRL write • RDRF is the Receive Data Register Full flag. • set by hardware if a received character is ready to be read • if set, the software read next into from SCIDRL • cleared by two-step software sequence • first reading SCISR1 with RDRF set • then SCIDRL read Nachiket M. Kharalkar

33. Transmitting in asynchronous mode Data and shift registers implement the serial transmission. • The software writes to SCIDRL, then • 8 bits of data are moved to the shift register • start and stop bits are added • shifts in 10 bits of data one at a time on TxD line • shift one bit per bit time (=1/baudRate) Nachiket M. Kharalkar

34. Receiving in asynchronous mode Data register shift registers implement the receive serial interface • The receiver waits for the 1 to 0 edge signifying a start bit, then • shifts in 10 bits of data one at a time from RxD line • shift one bit per bit time (=1/baudRate) • start and stop bits are removed • checked for noise and framing errors • 8 bits of data are loaded into the SCIDRL Nachiket M. Kharalkar

35. Three receive data frames result in an overrun (OR) error • If there is already data in the SCDR when the shift register is finished, it will wait until the previous frame is read by the software, before it is transferred. • An overrun occurs when there is one receive frame in the SCDR, one receive frame in the receive shift register, and a third frame comes into RxD. Nachiket M. Kharalkar

36. A device driver is a collection of software functions that allow higher level software to utilize an I/O device. • Collection of public methods (subroutines) • SCI_Init • SCI_InChar • SCI_OutChar • Collection of private objects (subroutines, globals, I/O ports) • SCICR2 • SCIBD • SCISR1 • SCIDRL • Complexity abstraction • divide a complex problem into simple subcomponents • Functional abstraction • divide a problem into modules • grouped by function Nachiket M. Kharalkar

37. SCI I/O Programming ; Initalize 9S12C32 SCI at 250000 bps ; Inputs: none ; Outputs: none ; Errors: none ; assumes 4MHz E clock (PLL not activated) SCI_Init movb #$0c,SCICR2 ;enable SCI TE=RE=1 movw #1,SCIBD ;250000 bps ;baud rate (bps) = 250000/BR rts Nachiket M. Kharalkar

38. SCI_InChar Busy‑waiting, gadfly, or polling are three equivalent namessoftware continuously checks the hardware status waiting for it to be ready Nachiket M. Kharalkar

39. SCI_OutChar Nachiket M. Kharalkar

40. ASCII strings • Stored with null-termination • In C, the compiler automatically adds the zero at the end • In assembly, the zero must be explicitly defined Msg fcc “EE319K is fun” fcb 0 Msg2 fcb “EE319K is fun”,0 Nachiket M. Kharalkar

41. Strings & Arrays • A string is a data structure • with equal size elements • only allows sequential access • always read in order from the first to the last. • An array is a data structure • with equal size elements • allows random access to any element in any order Nachiket M. Kharalkar

42. A variable length string contains ASCII data Nachiket M. Kharalkar

43. SCI Demo Nachiket M. Kharalkar