Microchip Technology dsPIC30F - Page 261

© 2004 Microchip Technology Inc. DS70059C-page 12-19
Section 12. Timers
Timers
12
12.10.2 Synchronous Counter Mode
The 32-bit timer operates similarly to a 16-bit timer in Synchronous Counter mode. Example 12-6
shows how to configure a 32-bit timer in Synchronous Counter mode. This example assumes
Timer2 is a Type B time base and Timer3 is a Type C time base.
Example 12-6: Initialization Code for 32-bit Synchronous Counter Mode Using an
External Clock Input
; The following code example will enable Timer2 interrupts, load
; the Timer3:Timer2 Period register and start the 32-bit timer
; module consisting of Timer3 and Timer2.
; When a 32-bit period match interrupt occurs, the user must clear
; the Timer3 interrupt status flag in the software.
CLR T2CON ; Stops any 16/32-bit Timer2 operation
CLR T3CON ; Stops any 16-bit Timer3 operation
CLR TMR3 ; Clear contents of the Timer3 timer register
CLR TMR2 ; Clear contents of the Timer2 timer register
MOV #0xFFFF, w0 ; Load the Period Register3
MOV w0, PR3 ; with the value 0xFFFF
MOV w0, PR2 ; Load the Period Register2 with value 0xFFFF
BSET IPC1, #T3IP0 ; Setup Timer3 interrupt for
BCLR IPC1, #T3IP1 ; desired priority level
BCLR IPC1, #T3IP2 ; (this example assigns level 1 priority)
BCLR IFS0, #T3IF ; Clear the Timer3 interrupt status flag
BSET IEC0, #T3IE ; Enable Timer3 interrupts
MOV #0x801A, w0 ; Enable 32-bit Timer operation and start
MOV w0, T2CON ; 32-bit timer with prescaler settings at
; 1:8 and clock source set to external clock
; Example code for Timer3 ISR
__T3Interrupt:
BCLR IFS0, #T3IF ; Reset Timer3 interrupt flag
; User code goes here.
RETFIE ; Return from ISR