The following information was extracted from the September 1998 Electronics Now Magazine. The author of the article was Michael A. Covington. In Michael's article he acknowledges the contribution of David Tait in regards to the "TOPIC" program. This project provides the beginning of a Learning Series on PIC micro controller. I will be providing other projects based on PIC in the future and therefore this project, PIC Programmer, is necessary for any future projects. It will allow you to program a PIC to perform functions that in the past would require numerous IC chips.
What is a PIC?. Well, like other micro controllers it is a tiny computer with CPU, ROM, RAM, and I/O circuits all on one chip. I will be focusing my projects on the inexpensive PIC's that are on the market. The chips that I will be using will be 16C84, 16F83 and 16F84. These chips are around $6.00. Because the ROM inside the chips are electrically erasable, the same PIC can be reprogrammed many times for different types of projects. Any information stored in the PIC will be held for more then 40 years, without power applied, until it is electrically erased. Unlike other microcontrollers, these PIC's do not require quartz crystals or resonators for their clock; you can simply use a resistor and capacitor as the oscillating elements.
The project presented here will provide you with the ability to program a PIC from your parallel printer port on your PC computer. To program a PIC is relatively simple. A standard 5 volt DC supply voltage is connected to pin 14 and ground is connected to pin 5. Now bring the voltage on pin 4 to between 12 and 14 volts dc. The data is clocked in one bit at a time through pins 13 and 12. The data itself is sent to pin 13. Once the bit is ready, the voltage on pin 12 is raised to 5 volts for at least 0.1 microseconds before being lowered back to ground. The data that was sent to the chip can sent back out of the chip on pin 13 to verify he accuracy.
From : http://home.maine.rr.com/randylinscott/aug20.htm