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TACTL = TASSEL_2 |MC_2 | ID_0 | TAIE; // SMCLK
// up mode to 0xFFFF
The capture unit captures the TAR register value to the TACCR1 register when it detects a low-to-high transition at the TA1 input. What is the value to write to the configuration register?
TACCTL1 = CCIS_0 | CAP | CCIE;
// Capture on rising edge,// TACCR1 input signal selected,
// Capture mode,// Capture/compare interrupt enable.
Determine the maximum and minimum frequency values detected. Note that these values do not take into account the execution time of the application. The PWM signals should be applied at frequencies well below the maximum value determined.
Maximum frequency value: ____________
Minimum frequency value: _____________
The TACCR1 capture unit is configured to generate an interrupt when it detects a low-to-high transition. What is the value to write to the configuration register?
TACCTL1 |= CM1
These ports perform special functions. Thus, the Port P3.5 is configured as an output, selected by the special function TB4, with the values:
// TB4 configuration (Port3)
P3SEL = 0x20; // P3.5 as special function (TB4)P3DIR = 0x20; // P3.5 as output
The Port P1.2 is configured as input, with the special function TA1, using the values:
// TA1 (TACCR1) configuration (Port1)
P1SEL = 0x04; // P1.2 as special function (TA1)P1DIR = 0x00; // P1.2 as input
// 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
Without a frequency generator, the Timer_B generates a PWM signal at the TBCCR4 unit output that can be fed back to Timer_A TACCR1 capture unit input. These two pins must therefore be connected together. By default, the PWM signal frequency is 200 Hz. Add a breakpoint at the line of code belonging to the Basic Timer1 ISR to modify this value.
TBCCR0 = 7995392/read_data;
If the variable
read_data has the value 200, it will generate a 200 Hz frequency. The value of this variable can be changed by associating a breakpoint to that line of code. Before the line of code is executed, the value of the data file is read and assigned to the variable
read_data . The signal will oscillate at the desired frequency, loading the value in TBCCR0. The breakpoint configuration is as follows:
- Action: read data from file
- File: address of the data file (example in freq.txt)
- Wrap Around: activate this option to restart reading at the beginning
- Start address:&read_data
- Length: 1 in order to read a value from the file each time
The operation of the application can be verified using a frequency generator. The generator should generate a PWM signal with voltage and frequency values compatible with the device’s input (2.5 to 3.3 volts).
The PWM signal applied to the TA1 input can be viewed using an oscilloscope, connected to pin 3 of Header 2. Perform this task and confirm the values present at the LCD.
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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