Active low transmitter question

[LEDave]

Here's the Rx schematic. When an Rx is received it outputs 5v onto the corresponding pin, which will then be read by the pic.

My question now is (and this should have been the question all along):

On the 12F683 pic I need to set a Tris pin to INPUT and read the pin for state change from LOW to High as the Rx is received.

TRISIO = %00000001 'Set to Input

TestRx 'LABEL
Do SomeThing 'LABEL

TestRx
IF
GPIO.0 = 0 THEN TestRx 'Nothing has happened continue to loop and check for state change

IF

GPIO.0 = 1 then DoSomeThing

DoSomeThing

Set alarm off in this case........

So, here's the $64k question from me: How do I hold GPIO.0 LOW until a 5v Rx is received? Is it a pulldown resistor?