RS232 Interface Scavenges Energy For Connected Devices

摘要

To convert the microcontroller's returning logic-level signal (TIN) to an RS232 signal, a non-inverting, tri-state output buffer (U2) and a pull-up resistor first expand the signal's voltage to range from GND to VPOS. Transistor Q2, a P-type enhancement MOSFET, then inverts and expands this intermediate signal to an output signal (RXD) that ranges between VNEG and VPOS.