How does this board achieve communication without a line driver?

Started by Fixxie, June 21, 2017, 02:19:23 am

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Fixxie

All the develooment boards I have seen yet with serial communication support usually have MAX232 line trasceiver. However, I have come across this Olimex PIC-LCD development board that does not have it. Rather, it seems to use discrete components to achieve the same aim. Below is the schematic. The RXD and TXD are connected to the PIC:



I am trying to understand how this works. For received data we would need to clamp the voltage to Vcc. For transmitted data we need to amplify the signal. I vaguely understand that there would be a simple clamp diode for the received data and a charge pump made up of capacitor and diode for the transmitter. The transistors are resistors are confusing me. What purpose do they serve?