Transcript Unit 12 part 1

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
Frequency
F1
Output 6
Frequency
F2
1 Sec
Output 4
1 Sec
Output 4
Output 6
Frequency
F3
1 Sec
Output 4
Output 6
Frequency
F4
1 Sec
Output 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 freerunning counter
- Unit clock period is therefore 1 microsecond
Frequency of Notes
Note
Frequency
Period (usec)
C
262
3816.8
C#
272
3676.5
D
294
3401.4
D#
311
3215.4
E
330
3030.3
F
349
2865.3
F#
369
2710.0
G
392
2551.0
G#
415
2409.6
A
440
2272.7
A#
466
2145.9
B
495
2020.2
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;
----
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
---}
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
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
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
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
}
}
ECE 371 Timer Example
Rotary Dial Telephone
Decode Dial Digits
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.
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
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
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
3,12510 = 0x0C35
//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
}
// 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
}
}
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)
Timer Compare Force Register
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
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”
Output Compare 7 Mask Register
Output Compare 7 Data Register
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
OC7
OC4
OC2
0
0
0x4000
0x8000
TCNT
0xC000
0
0x4000
TCNT
0x8000
0xC000
0
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;
“Alarm Clock” values for Channels 2, 4, 7
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
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
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
Pulse Accumulator Enable
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.
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
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.
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
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.