how to change from internal clock to external clock counter of PIC32

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C

Hi i got the code to program a timer using a internal clock of PIC32 microcontroller using timer 1. I'm using a 16-bit synchronous external clock counter to do a counting for incoming data signal from AD9883A video analog to digital convertor. I will like to know which part of it i need to change and how do i include the input of the signal that i need to count.. Here is the code...

#include <plib.h>
#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, #pragma config FWDTEN = OFF
#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_8

// Let compile time pre-processor calculate the PR1 (period)
#define SYS_FREQ 			(80000000L)
#define PB_DIV         		8
#define PRESCALE       		256
#define TOGGLES_PER_SEC		1
#define T1_TICK	    (SYS_FREQ/PB_DIV/PRESCALE/TOGGLES_PER_SEC)

int main(void)
{
    SYSTEMConfig(SYS_FREQ, SYS_CFG_WAIT_STATES | SYS_CFG_PCACHE);
	
    //configure Timer 1 using internal clock, 1:256 prescale
    OpenTimer1(T1_ON | T1_SOURCE_INT | T1_PS_1_256, T1_TICK);
    
    // set up the timer interrupt with a priority of 2
    ConfigIntTimer1(T1_INT_ON | T1_INT_PRIOR_2);
    
    // enable multi-vector interrupts
    INTEnableSystemMultiVectoredInt();
    // configure PORTD.RD0 = output
    mPORTDSetPinsDigitalOut(BIT_0);
    while(1);
}
void __ISR(_TIMER_1_VECTOR, ipl2) Timer1Handler(void)
{
    // clear the interrupt flag
    mT1ClearIntFlag();
    // .. things to do
    // .. in this case, toggle the LED
    mPORTDToggleBits(BIT_0);
}</plib.h>