How does the PIC Programmer work?
When the PC drives the DTR signal line to a negative voltage, the 13V zener diode is forward biased. Current flows from GND through the zener diode, charging the 470uF capacitor (C1). The 10K resistor (R11) limits the current into C1 so that we don’t stress the PC’s serial port (usually current limited anyway on most PCs). Once the capacitor is fully charged and the user tells the programming software to begin, the PC drives the DTR signal line to a positive voltage. At this point, the capacitor C1 has double the voltage when measured from GND to VPP (charge pump). The zener diode is now reverse biased and acts as a voltage regulator, preventing the voltage on MCLR from going above 13V. The resistor R11 now limits the current coming out of the capacitor so that we don’t drain all of our excess charge through the zener diode immediately. Since the PIC chip consumes very little current, this charge pumped capacitor design will provide high voltage on the MCLR line for several seconds bef
