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Unit 12

Unit 12. Timer Examples. Example – Music Generation. Channel 6 – Set up as a timer Output to Generate Square Waves Channel 4 – Set up as a timer Output to control the length of each tone. Free-running counter will have a time resolution of 1 Microsecond. Music Generation. Output 6

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Unit 12

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  1. Unit 12 Timer Examples

  2. Example – Music Generation • Channel 6 – Set up as a timer Output to Generate Square Waves • Channel 4 – Set up as a timer Output to control the length of each tone. • Free-running counter will have a time resolution of 1 Microsecond

  3. Music Generation Output 6 Frequency F1 Output 6 Frequency F2 Output 6 Frequency F3 Output 6 Frequency F4 1 Sec Output 4 1 Sec Output 4 1 Sec Output 4 1 Sec Output 4

  4. Details of implementation • Channel 4 is used to generate an Interrupt every 50 milliseconds • 20 interrupts = 1 second • Select a new frequency for Channel 6’s output at end of each 1 second interval • Prescale value of 2 is used to provide 1 MHZ clock to free-running counter - Unit clock period is therefore 1 microsecond

  5. Frequency of Notes

  6. Software Initialization ---- // forward references to interrupt service routines void oc6_isr(void) __attribute__ ((interrupt)); // IC6 Interrupt void oc4_isr(void) __attribute__ ((interurpt)): // IC4 interrupt ---- ---- // global variables – period of each note unsigned int freq[12] = 3817, 3677, 3401, 3215, 3030, 2865, 2710,2551, 2410, 2273, 2146, 2020; // global variable - song unsigned char music[13] = 0,1,2,3,4,5,6,7,8,9,10,11,0xFF; //index of notes in song--12 notes plus end flag ---- unsigned int tp4 = 50000; //50 milliseconds unsigned int tp6 = 3817/2; // half period for C note unsigned idx1=0, idx2=0; ----

  7. Main Program int main() { --- TSCR2 = 0x01; // 1 usec resolution with TNCT,using // prescale factor of 2 on internal 2 MHz clock // No TOF Interrupt ---- // initialize Channel 6 for generating square wave ---- // initialize Channel 4 for control of interval length for each note --- ENABLE(); // enable interrupts ---- }

  8. Initialize Channel 6 /* Initialize Output Compare Channel 6 Complement on Each Compare Timer has been initialized */ TIOS = TIOS | 0x40: // Set Channel 6 to Output Compare – Bit 6 // TIOS = x1xx xxxx TCTL1 = (TCTL1&0xCF) | 0x10; // Toggle Output Line 6 (square wave) // TCTL1 = xx01 xxxx TFLG1 = 0x40; // Clear Channel 6 Flag TC6 = TCNT + tp6; // Complement in tp6 Seconds Set earlier to be half period of C Note

  9. Using Interrupts for Channel 6 Task SETVECT(0xFFE2, oc6_isr); // set interrupt vector TIE = TIE | 0x40; // Enable Channel 6 Interrupt ---- ---- void oc6_isr(void) {// Period of square wave is 2*tp6 TC6 = TC6 + tp6; // Next interrupt set up for tp6 from now TFLG1 = 0x40; // Clear Channel 6 Flag }

  10. Initialize Channel 4 /* Initialize Output Compare Channel 4 Complement on Each Compare Timer has been initialized */ TIOS = TIOS | 0x10: // Set Channel 4 to Output Compare – Bit 4 // TIOS = xxx1 xxxx TCTL1 = (TCTL1&0xFC) | 0x01; // Toggle Output Line 4 // TCTL1 = xxxx xx01 – Toggle Pin 4 TFLG1 = 0x10; // Clear Channel 4 Flag TC4 = TCNT + tp4; // Complement in tp4 Seconds // tp4 = 50 000 microseconds

  11. Using Interrupts for Channel 4 Task SETVECT(0xFFE6, oc4_isr); // set interrupt vector TIE = TIE | 0x10; // Enable Channel 4 Interrupt ---- ---- initially set to 50000 void oc4_isr(void) {TC4 = TC4 + tp4; // Complement T from now and generate // interrupts 20 times per second TFLG1 = 0x10; // Clear Channel 4 Flag idx0++; // Count Channel 4 interrupts up to 20 if(idx0>20) initially set to 0 { // 1 second has elapsed idx0=0; idx1++; //bump up index to next note if (music[idx1]==0xFF)idx1=0; tp6 = freq[music[idx1]]/2; // select period of next note } }

  12. ECE 371 Timer Example Rotary Dial Telephone Decode Dial Digits

  13. Rotary Dial • If not using phone, telephone presents an open circuit and no current flows. • If telephone is in use, then current flows since there is a DC voltage of 48 volts on line. Phone appears as a 600 to 900 Ohm resistor. • Rotary dial opens the line for 1/20 seconds for each pulse.

  14. Rotary Dial Telephone 1 pulse for digit 1 3 pulses for digit 3 2 pulses for digit 2 .3 sec .1 sec Old Rotary Dial Phones generated 1 to 10 pulse each time a number Was dialed. The pulse rate was 10 pulses per second with a .3 second Interval between successive digits. The Dial opens the line for about 1/20 second for each digit. Let Channel 0 detect and count the 0->1 transitions Let Channel 1 detect the gap between digits

  15. Initialization • Select Channel 0 as Input • Select Trigger on 0->1 Edge • Select Channel 1 as Output • For Bus Clock = 2 MHZ, Select Prescale bits to 0b111 for a Prescale factor of 128

  16. 2,000,000 15,625 = frequency of scaled clock = 128 1 = period of divided clock 15,625 Let x = initialization value for Counter 1 Solve for x: 1 x = .2 15,625 x = .2 (15,625) = 3,125 3,125 = 0x0C35 10

  17. //Global Variables unsigned int idx0 = 0; //count of pulses for each digit dialed unsigned int idx1 = 0; //count of number of digits dialed unsigned char digit[20]; //accept maximum of 20 dialed digits --- //interrupt handler for channel 0 void ic0_isr(void) { TFLG1 = 0x01; // clear channel 0 flag TC1 = TC0 + 0x0C35; // Insert new time in channel 1 (for an interrupt in .2 sec) // If channel 1 interrupt before channel 0, then gap found idx0++; // increment pulse counter TFLG2=0x02; // clear channel 1 flag TIE = TIE | 0x02; // enable interrupts from channel 1 }

  18. // channel 1 interrupt service routine // Gap between digits is found void oc1_isr(void) {if(idx1<20) {// prevent buffer overflow digit[idx1++] = idx0; // save count idx0 = 0; TFLG1 = 0x02; // clear flag TIE = TIE & 0xFD; // disable interrupts } }

  19. Other Timer Options • Force Output Action of Selected Channels to Occur Immediately • Use Successful Channel 7 Condition to Cause Other Selected Channel Outputs to Take on Specified Values • “Pulse Accumulator” Mode for Implementing Event Counter or Counter with Gated Clock • Let Two Counters Share an Input Pin for Detecting an Input Condition (rise,fall, or toggle)

  20. Timer Compare Force Register

  21. CFORC Example // Channel 6, 3, 2, 0 are selected as Outputs CFORC = 0x05; // Force Output Actions on Channel 0 and 2 // Does not set flags for interrupt request // CFORC = 0x44; // Force Output Actions on Channel 3 and 6 // Does not set flags for interrupt request

  22. Output Compare on Channel 7 • Option of sending new values to all or any subset of Output Pins • OC7M Selects Output Pins • OC7D Select New State of Selected Pins • Can Reset TNCT if TCRE=“1”

  23. Output Compare 7 Mask Register

  24. Output Compare 7 Data Register

  25. Example of Application of “Output Compare on Channel 7”: Generate Pulse Width Modulation (PWM) Signals • Period Can Be Specified by OC7 • Width of Pulse Generated at Output I Can Be Specified by OCi

  26. OC7 OC4 OC2 0 0x4000 0x8000 0xC000 0x4000 0x8000 0xC000 0 TCNT 0 TCNT 0

  27. Example OC7 and TCRE=1 TIOS = TIOS | 0x94 ;//Select Channel 2, 4, 7 as Outputs OC7M = 0x14; // Select Channel 4 and 2 OC7D = 0x04; // Clear Channel 4 and Set Channel 2 TC7 = 0xC000; TC4 = 0x4000; TC2 = 0x8000; TCTL1= (TCTL1&0x3C) | 0x41; //0b0100 0001 - Ch 7 and 4 // TCTL1 = 01xx xx01 - toggle Ch 7 and 4 TCTL2= (TCTL2&0xCF) | 0x10; //0b0001 0000 - Ch2 // TCTL2 = xx01 xxxx - toggle Ch 2 TSCR2=0x09; // 0b00001001 – TCRE=1, Prescale=1 “Alarm Clock” values for Channels 2, 4, 7

  28. Pulse Accumulators • 4 8-bit Pulse Accumulator • PAC0, PAC1, PAC2, PAC3 • Pin 0, 1, 2, and 3 of Port T serve as inputs for PACO, PAC1, PAC2, and PAC3 • Accumulators are incremented on selected edge on pin • TCTL4 selects edge detector algorithm • Rise, fall, either

  29. Delay Algorithm • If 0->1 is selected edge, then input must be 1 after delay for Pulse Accumulator to be incremented • If 1->0 is selected edge, then input must be 0 after delay for Pulse Accumulator to be incremented

  30. Pulse Accumulator Enable

  31. Modulus Down Counter • 16-Bit Down-Counter That Can Be Initialized to Any 16-Bit Value • When counter reaches 0x0000: - It sets a flag and can cause an interrupt - If is reloaded with its starting value and starts counting down again - In “Latch Mode,” values in the 8-bit Pulse Accumulators and 16-bit values in Input Capture Registers are latched into their holding registers, and the the 8-bit Pulse Accumulators are cleared.

  32. Buffered Mode • Holding registers for Input Capture and Pulse Accumulators are enabled. • Permits 2 input captured values prior to interrupt • Enabled by setting BUFEN=“1” in ICSYS • Channels 0, 1, 2, and 3 support Buffered Mode

  33. Buffered Mode (cont) • Latching mode controlled by LATQ bit in ICSYS - LATQ = 0: Queue Mode: Latch on second edge (second pulse) - LATQ = 1: Latch Mode: Latch when Modulus Down Counter = 0 Note: When LATQ = 1 in Buffered Mode, a latching operation can be forced by setting a “1” to the ICLAT in the MCCTL control register.

  34. SH37 – Pin 3 in input to Channel 3 and 7 concurrently SH26 – Pin 2 is input to Channel 2 and 6 concurrently SH15 – Pin 1 is input to Channel 1 and 5 concurrently SH04 – Pin 0 is input to Channel 0 and 4 concurrently

  35. 1 = Latch Mode is enabled. Latching occurs when modulus down-counter reaches zero or a zero is written into the count register MCCNT. When a latching event occurs, the contents of the Input Capture Registers and the 8-bit pulse accumulators are transferred to their Holding Registers and the 8-bit Pulse Accumulators are cleared.

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