RS232 with single power supply

In most personal computers, the power supply provides +5 V and ±12 V lines. The positive 12 V line is needed for the disk drives, and the ±l2 V für the RS232 interface. Over the past few years, ICs have become available (such as the MAX232) that can drive serial channels (which need ±12 V) from a single +5 V line.