详细讲述了RS232，RS485，RS422电平间的不同，及各电平的特点等问题。

The MAX481E, MAX483E, MAX485E, MAX487E–MAX491E, and MAX1487E are low-power transceivers for RS-485 and RS-422 communications in harsh environments. Each driver output and receiver input is protected against ±15kV electrostatic discharge (ESD)