MSP430F5438 Study Notes 1-Timer

    This is the default mode of the timer. When in comparison mode, the hardware related to the capture mode stops working. If the timer interrupt is enabled at this time, then the timer final value is set (write the final value into TACCRx), and the timer is enabled, when the value of TAR increases to TACCRx, the interrupt flag CCIFGx is set to 1, and an interrupt is generated. If the interrupt is not enabled, only the interrupt flag CCIFGx is set to 1.

Example: The comparison mode is like the 51 MCU. It is necessary to be able to set the time interval by software to generate interrupts to handle some things, such as keyboard scanning. It can also be combined with signal output to generate timing pulse generators and PWM signal generators. For example: continuously load TACCRx, start the timer, and compare TAR with TACCRx to generate interrupt processing.

Capture Mode:

    Use the rising edge, falling edge, or rising and falling edge trigger of the external signal to measure external or internal events, and can also be stopped by software. The capture source can be selected by CCISx CCIxA, CCIxB, GND, VCC. After the capture is completed, the corresponding capture flag CCIFGx is set

Application of capture mode:

    Use the capture source to trigger the capture of the TAR value, and save each captured value to TACCRx. You can read the value of TACCRx at any time. TACCRx is a 16-bit register. The capture mode is used for precise positioning of events, such as measuring time, frequency, speed, etc.

Example: Use the values ​​of two captures to measure the pulse width. Or capture any edge, CCISx = "11" (input selects VCC), so that the capture condition is generated when VCC and GND switch.

Combined use: Asynchronous communication

The comparison mode and capture mode are used at the same time to realize UART asynchronous communication. That is, the comparison mode of the timer is used to simulate the baud rate of the communication sequence to send data, and the capture mode is used to receive data, and the comparison mode is switched in time to select and adjust the receiving baud rate of the communication, so as to achieve the purpose of several byte

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The pulse width is measured by combining the MSP430 single-chip microcomputer timer A with the capture/compare function module.

     This example uses the CCI1A port of timer A (such as the P1.2 pin of MSP430F14X) to capture the pulse level jump of the external input, and combines it with a simple software algorithm to achieve the measurement of pulse width. In actual applications, the pulse width can be calculated based on the three variables start, end, and overflow in the example. This functional module has a high application value in actual product applications.

2- Routine

#include

unsigned int start,end;

unsigned char overflow;

void main (void)

{

WDTCTL  = WDTPW+WDTHOLD;                  // Turn off the watchdog timer

P1DIR = BIT0+BIT4;                       //Set P1.0 direction to output

P1SEL = BIT2;                            //Set P1.2 port to be used as a functional module

TACTL = TASSEL0+TACLR+TAIE+MC1;          //Select ACLK as the clock signal of timer A, and set the counting mode of timer A to continuous increment mode

CCTL1 = MC0+SCS+CAP+CCIE;                // Input rising edge capture, CCI0A is the capture signal source

_EINT();                                 //Interrupt enable

while(1);                                //LOOP

}

#pragma vector=TIMERA1_VECTOR             //Timer A interrupt processing

__interrupt void timer_a(void)

{

switch(TAIV)                             //vector query

{  case  2:                               //Capture interrupt

if(CCTL1&CM0)                     // rising edge

{

CCTL1=(CCTL1&(~CM0))|CM1;      //Change to falling edge trigger

start=TAR;                     //Record initial time

overflow=0;                    //Reset overflow count variable

}

else if (CCTL1&CM1)               // falling edge

{

CCTL1=(CCTL1&(~CM1))|CM0;     //Change to rising edge trigger

end=TAR;                     // Use start, end, overflow to calculate pulse width

}

break;

case 10:                            //Timer overflow interrupt

overflow++;

break;                           // Overflow count plus 1

default:break;

}

}

// End of routine