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The ports connected to the LEDs, buttons and buzzer are then initialized.
Finally, the interrupts are activated, and the application waits for the execution of one of two interrupts.
The Basic Timer1 interrupt executes at a frequency of once every second. When this interrupt is occurs, it begins by switching the state of LED1 and LED2. Afterwards, it accesses the memory to fetch the next musical note to be performed. The routine ends with memory pointer management.
The Port 1 ISR begins by evaluating the source of the interrupt. The sound volume is reduced if the button SW1 is pressed. The sound volume is increased if button SW2 is pressed.
It is the responsibility of Timer_B to produce the PWM signal that activates the Buzzer. Timer_B counts until the value contained in the TBCCR0 register is reached. It does not generate an interrupt, and must be sourced by SMCLK clock signal:
TBCTL = TBSSEL_2 | CNTL_0 | TBCLGRP_0 |MC_1 | ID_0;
Each PWM signal produced by Timer_B corresponds to a musical note. The relationship between the frequency and the musical note is given in Table 1.
| Note | SI0 | DO | RE | MI | FA | SOL | LA | SI | DO2 |
| Freq [Hz] | 503 | 524 | 587 | 662 | 701 | 787 | 878 | 1004 | 1048 |
Timer_B has a frequency clock input equal to 7.995392 MHz.
The value to write in the TBCCR0 register in order to generate the desired frequency is:
// TBCCR0 value of the musical notes
#define SI0 15895#define DO 15258
#define RE 13620#define MI 12077
#define FA 11405#define SOL 10159
#define LA 9106#define SI 7963
#define DO2 7629TBCCTL4 = OUTMOD_3; // CCR4 interrupt enabledTBCCR4 = space[0]/2;
TACTL = TASSEL_2 |MC_2 | ID_0 | TAIE; // SMCLK, continuous mode up to 0xffff
TACCTL1 = CM1 | CCIS_0 | CAP | CCIE;// Capture on rising edge, Cap mode,// Cap/Com int. enable, TACCR1 input signal selected//*********************************************************
// Timer A ISR//*********************************************************
#pragma vector=TIMERA1_VECTOR__interrupt void TimerA1_ISR (void)
{switch (TAIV)
{case TAIV_TACCR1:
if (capture == 0){T1 = TACCR1;
flag = 1;capture = 1;
}else {
if (flag == 1) {T2 = TACCR1;
if (T2>T1)
T = T2-T1;}
else{TAR = 0;
}capture = 0;
flag = 0;}
break;
case TAIV_TACCR2:
break;case TAIV_TAIFG:tick++;
if (tick == 60){LCD_freq();
tick = 0;}
if (flag == 1)flag = 0;
break;
default:
break;}
}
The Basic Timer1 generates an interrupt once every second. It uses two counters in series, where the BTCNT2 counter input uses the BTCNT1 counter output divided by 256. The BTCNT1 counter input is the ACLK clock signal with a frequency of 32.768 kHz.
If BTCNT2 counter selected output is divided by 128, what is the time period associated with the Basic Timer1 interrupt? _________
What are the values to write to the configuration registers?
BTCTL = BTDIV | BT_fCLK2_DIV128; // (ACLK/256)/128
IE2 |= BTIE; // enable BT interrupt//*********************************************************// Basic Timer ISR. Run with 1 sec period
//*********************************************************#pragma vector=BASICTIMER_VECTOR
__interrupt void basic_timer_ISR(void){
unsigned int read_data; // read data from file , frequency in kHzP2OUT^=0x06; // toogle LED1 and LED2counter++;if (counter == 5){
counter = 0;read_data = 200;
TBCCR0 = 7995392/read_data;TBCCR4 = TBCCR0/2;
}}
// SW1 and SW2 configuration (Port1)
P1SEL&= 0x00; // P1.0 and P1.2 I/O
P1DIR&= 0x00; // P1.0 and P1.2 as inputs
P1IFG = 0x00;P1IES&= 0xFF // high-to-low transition interrupt
P1IE |= 0xFF; // enable port interrupts// LED1 and LED2 configuration (Port2):P2DIR |= 0x06; // P2.2 and P2.1 as outputs
P2OUT = 0x04; // LED1 on and LED2 off// Buzzer port configuration (Port3)P3SEL |= 0x20; // P3.5 as special function
P3DIR |= 0x20; // P3.5 as digital output
FLL_CTL0 |= DCOPLUS + XCAP18PF; //DCO+ set,freq=xtal*D*N+1
SCFI0 |= FN_4; // x2 DCO freq, 8MHz nominal DCOSCFQCTL = 121; // (121+1) x 32768 x 2 = 7.99 MHz
The MCLK, SMCLK and ACLK system clocks are available at ports P1.1, P1.4 and P1.5 respectively. These ports are located on the SW2, RESET_CC and VREG_EN lines, which are available on the H2 Header pins 2, 5 and 6. All these resources are available because the Chipcon RF module is not installed and SW2 is not used.
Using the Registers view, set bits 1, 4 and 5 of P1SEL and P1DIR registers to choose the secondary function of their ports, that is, configured as outputs. Connect an oscilloscope probe at these positions to monitor the clock signals.
What are the values measured for each of the system clocks?
ACLK: _____________________
SMCLK: ____________________
MCLK: _____________________
With the help of an oscilloscope, it is possible to evaluate the operation of the application. Alternatively, it is possible to listen to the sound produced. By removing jumper JP1 and connecting the oscilloscope to this pin, it is possible to view the PWM signal produced by the microcontroller. The duty-cycle can be reduced or increased by pressing the push buttons SW1 and SW2.
All Port P1 interrupt lines share the same interrupt vector. The decoding is done through the P1IFG register.
This process can be observed by entering a breakpoint at the first line of the ISR code.
Execute the application.
The application’s execution is suspended at the breakpoint by pressing either button SW1 or SW2. From this point onwards, run the lines of code step-by-step and observe changes in the register values.
The power consumption was discussed in the previous point. The electrical power required by the system during operation is measured by replacing the jumper on the Header PWR1 by an ammeter, which indicates the electric current taken by device during operation.
What is the value read? __________
This example and many others are available on the MSP430 Teaching ROM.
Request this ROM, and our other Teaching Materials here (External Link)
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