By "rate", did you mean the number of people passed in one minute?

IF yes, then use Timer1 module of the PIC at 1:8 scale and have 500ms timing interval. This way, you can have Timer1 module timing in the background while you can at the sametime have your counting in the foreground.

OR

You can just use simple PAUSE command to create 1 minute timing interval and have your counting in a WHILE statement.

For example,
Code:
CountPin VAR PORTA.0
Timing   VAR WORD
Counter  VAR WORD
Timing = 0
Counter= 0

Start:

WHILE Timing < 6000
	IF CountPin = 0 THEN
		WHILE CountPin = 0 : WEND

		Counter = Counter + 1   'Number of people Passed
		Timing  = Timing  + 1	'Timing: 6,000x10ms=60,000ms (1 min) 
		PAUSE 10

	ENDIF
WEND

Timing = 0

Goto Start