This is a basic RS-232 transmit/receive circuit that is necessary for PIC microcontrollers to reliably communicate with a PC serial port.
The RS-232 specification requires that the signal levels be ±3-15 Volts and unfortunately the PIC microcontroller operates at TTL levels (0-5 Volts). The MAX233 is a nice IC that allows you to convert microcontroller voltages to RS-232 compatible levels with no required external components.
Authored by
Steven Cholewiak at
Semifluid, Added: 22 Dec 2006
http://www.semifluid.com/RS-232_level_converter.html
