© 2004 Microchip Technology Inc. DS70059C-page 12-13
Section 12. Timers
Timers
12
Figure 12-4: Gated Timer Mode Operation
Example 12-4: Initialization Code for 16-bit Gated Time Accumulation Mode
TxIF
0001 0002
TMRx
1 Instruction Cycle (T
CY
)
00040003
TxCK pin
00050000
TxIF bit cleared by user in software.
; The following code example will enable Timer2 interrupts, load the
; Timer2 Period register and start Timer2 using an internal clock
; and an external gate signal. On the falling edge of the gate
; signal a Timer2 interrupt occurs. The interrupt service
; routine must clear the Timer2 interrupt status flag in software .
CLR T2CON ; Stops the Timer2 and reset control reg.
CLR TMR2 ; Clear contents of the timer register
MOV #0xFFFF, w0 ; Load the Period register with
MOV w0, PR2 ; the value 0xFFFF
BSET IPC1, #T2IP0 ; Setup Timer2 interrupt for
BCLR IPC1, #T2IP1 ; desired priority level
BCLR IPC1, #T2IP2 ; (this example assigns level 1 priority)
BCLR IFS0, #T2IF ; Clear the Timer2 interrupt status flag
BSET IEC0, #T2IE ; Enable Timer2 interrupts
BSET T2CON, #TGATE ; Set up Timer2 for operation in Gated
; Time Accumulation mode
BSET T2CON, #TON ; Start Timer2
; Example code for Timer2 ISR
__T2Interrupt:
BCLR IFS0, #T2IF ; Reset Timer2 interrupt flag
; User code goes here.
RETFIE ; Return from ISR
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