This simple circuit can be used to program the PIC16F84 and similar
"flash memory" type parts. It uses a cheap 555 timer IC to generate the
programming voltage from a +5V rail, allowing the circuit to be powered
from a computer’s USB port. The 555 timer (IC1) is configured as a
free-running oscillator, with a frequency of about 6.5kHz. The output of
the timer drives four 100nF capacitors and 1N4148 diodes wir-ed in a
Cockroft-Walton voltage multiplier configuration.
The output of the multiplier is switched through to the MCLR/Vpp pin of
the PIC during programming via a 4N28 optocoupler. Diodes ZD1 and D5
between the MCLR/Vpp pin and ground clamp the output of the multiplier
to about 13.6V, ensuring that the maximum input voltage (Vihh) of the
PIC is not exceeded. A 100kΩ resistor pulls the pin down to a valid
logic low level (Vil) when the optocoupler is not conducting. The
circuit is compatible with the popular "JDM" programmer, so can be used
with supporting software such as "ICProg" (see http://www.ic-prog.com).
Tidak ada komentar:
Posting Komentar