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attainable because of the complexity of modern PC hardware and the plethora of programming options possible in PIC microcontrollers. In the next two sections, I present a couple of the programmer projects that I have embarked upon. I m including them here because I think there are some useful functions that you may want to incorporate in your own designs and because I have a hope that one day somebody will come up with a perfect hobbyist programmer that can be built cheaply and easily, allowing hobbyists easy access to the PIC microcontroller without making a substantial investment in money or time.

These disasters can be avoided if you prepare for them ahead of time. Consider these suggestions every time you re conducting a presentation.

When I wrote the rst edition of this book, I ended up spending an unreasonable amount of time trying to come up with a programmer for it. The goal was to create a PIC16F84 programmer that would work with virtually all PCs, with a simple programming interface. As I was working through the book, I came up with three different programmers, using both the PC s parallel port and serial port, each one with some strengths and weaknesses. Usually the programmers were very inexpensive, but none of them was able to run on a reasonably wide variety of PCs. My nal solution to the problem was the YAP (Yet Another Programmer). This programmer used a PIC16C61 with an RS-232 interface that took a downloaded hex le and programmed it into the target PIC microcontroller as the le was downloaded. The programmer worked quite well though it only runs at 1200 bps, somewhat slower than other devices out there. The reason for 1200 bps was to make sure there would be enough time for the worst case programming of EPROM parts. Fig. 4.18 shows the assembled YAP-II programmer. The slowness of the operation was to ensure that data did not come in faster than the PIC MCU could program into the target device. The YAP approached the problem from the perspective of using the PC s RS-232 ports as the basic interface not only to the programmer but for programming timing as well. This had three advantages over the other methods tried. The rst was the use of an I/O port with standard timings while the communication voltages would have to be translated from RS-232 protocol to CMOS/TTL, the incoming

data rate could be used to time data going into the PIC microcontroller. The second advantage was the ability of PIC microcontroller applications to interface to standard ASCII terminal emulators and not require custom PC software that would have to be debugged in parallel with the PIC microcontroller application. Lastly, many people who wanted to learn about the PIC microcontroller but were not running an MS-DOS or Microsoft Windows PC could run the YAP on their hardware to develop their own applications. Once I had this concept, I created the following speci cations for the YAP programmer:

Able to program all mid-range parts (EPROM and Flash-based program memory) Able to take the programming signals and use them in ICSP applications Allow any RS-232 equipped host PC or workstation to program PIC microcontrollers Allow serial communications between the host PC or workstation and the executing application for debugging applications on the y

The result was the YAP, which really wasn t a bad design, but fell short in a number of areas. These included problems with the reset circuit that made programming EPROM parts unreliable, selecting parts that were dif cult for people to nd or expensive, and creating a form factor that made building sample applications more dif cult than it should have been. It did have some positive points, however, in terms of its ease of use and reliability for different PCs and workstations. I also created a Visual Basic interface, which makes using the YAP much easier than running it from a basic terminal emulator. Once the problem with the line-ending characters was resolved, the programmer itself was downloaded and built by a number of people, and Wirz Electronics has sold a large number of built and tested units with very few complaints. Taking this base, the programmer was enhanced into the YAP-II with the following features:

More reliable programming for EPROM parts Ability to program PIC12C5xx and PIC16C505 PIC microcontrollers as well as 28-

Eliminates some of the dif cult-to- nd/expensive parts Provides a better form factor for hobbyists and people learning the PIC microcontroller