Microchip Technology dsPIC33F Family Manual de usuario descargar pdf (Pagina 12)

dsPIC33F/PIC24H Family Reference Manual

11.4.2 Gated Timer Mode

When the Timer module operates with the internal clock (TCS = 0), Gated Timer mode can be

used to measure the duration of an external gate signal. In this mode, the timer increments by

one on every rising edge of the input clock as long as the external gate signal at the TxCK pin is

high. The timer interrupt is generated on the falling edge of the TxCK pin. Figure 11-5 illustrates

Gated Timer mode operation.

To configure the Gated Timer mode:

• Set the TGATE control bit (TxCON<6>) to enable gated timer operation

• Clear the TCS control bit (TxCON<1>) to select the internal clock source

Setting the TSYNC bit (TxCON<2>) has no effect because the internal clock is always

synchronized.

Example 11-2 illustrates the code sequence to measure the pulse-width (T1CK) in Gated Timer

mode.

Example 11-2: Initialization Code for 16-Bit Gated Timer Mode

Figure 11-5: Gated Timer Mode Operation

T1CONbits.TON = 0; // Disable Timer

T1CONbits.TCS = 0; // Select internal instruction cycle clock

T1CONbits.TGATE = 1; // Enable Gated Timer mode

T1CONbits.TCKPS = 0b00; // Select 1:1 Prescaler

TMR1 = 0x00; // Clear timer register

PR1 = 9; // Load the period value

IPC0bits.T1IP = 0x01; // Set Timer1 Interrupt Priority Level

IFS0bits.T1IF = 0; // Clear Timer1 Interrupt Flag

IEC0bits.T1IE = 1; // Enable Timer1 interrupt

T1CONbits.TON = 1; // Start Timer

/* Example code for Timer1 ISR */

void __attribute__((__interrupt__, no_auto_psv)) _T1Interrupt(void)

{

/* Interrupt Service Routine code goes here */

IFS0bits.T1IF = 0; // Clear Timer1 Interrupt Flag

}

Timer Clock

Input

(Internal)

TxIF

TMRx

PRx

Cleared by user software

TxCK

(Gate Input)

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 25 26

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Microchip Technology dsPIC33F Family Manual de usuario Pagina 12