Answer:+5V to +15V
Generation of RS-232 Voltage Levels
Drivers have to supply +5V to +15V for a logic 0 and -5V to -15V for a logic 1. This means that extra power supplies are needed to drive the RS-232 voltage levels. Typically, a +12V and a -12V power supply are used to drive the RS-232 outputs.
Explanation:
