Max232 is a converter IC and converts signals from a TIA-232(RS-232) serial port to signals suitable for use in TTL- compatible digital logic circuits, typically converts the RX, TX, CTS, RTS signals. This is a dual receiver or dual transmitter. It gives about ±7.5V TIA-232 Voltage level output from 5V input by on-chip charge pumps and external capacitors which makes it useful to implement TIA-232 in devices.
The receiver reduces TIA-232 inputs, which can be up to ±25V, to 5V TTL levels. The typical threshold and hysteresis of receiver is 1.3V and 0.5V respectively.