krise86, Depending on the capacitator values used with a MAX-232 the charge pump voltages should be around +-6 volts to +- 9 volts. The TRUE RS-232 spec calls out for mark,space voltages of +- 3 volts minimum... Some laptop computers now days do not meet the TRUE RS-232 spec limits as some only put 0 to +5 volts... That is why some laptop computers don't have a solid serial communications...

Dave Purola,
N8NTA