A charge pump voltage converter is used to generate the±10V supply for the RS-232 transmitter. This is done in two stages. First, the 5V input is doubled using a capacitor connected between pins C1+ and C1-. The +10V is then inverted by the capacitor connected between pins C2+ and C2- to produce the -10V supply. The receiver, on the other hand, uses an inverting level shifter to translate the higher voltage, dual polarity RS-232 signals into 5V logic levels.