Most of the i.c. comparators have a pull-down npn transistor whose emitter is tied to Vss, but no pull-up, so you have to wire an external resistor to some positive voltage source. The resistor value depends on what the output is driving, and how fast you want the output to switch high. If there is a lot of capacitance on the comparator's output pin, and you dont care how much power you burn, then 470 Ohm to +5V might be appropriate. If speed is less of an issue, and you are driving CMOS or other high-impedance loads, then 5K might be appropriate.