Page 47 - Amphibionics : Build Your Own Biologically Inspired Robot

Amphibionics 03 3/24/03 8:11 AM Page 26
Amphibionics
PIC 16F84 MCU
Microchip technology has developed a line of reduced instruction
set computer (RISC) microprocessors called the programmable
interface controller (PIC). The PIC uses what is known as “Harvard
architecture.” Harvard uses two memories and separate busses.
The first memory is used to store the program, and the other is to
store data. The advantage of this design is that instructions can be
fetched by the CPU at the same time that RAM is being accessed.
This greatly speeds up execution time. The architecture common-
ly used for most computers today is known as Von Neumann
architecture. This design uses the same memory for control and
RAM storage, and slows down processing time.
We will be using the PIC 16F84, shown in Figure 3.1, as the
processor for the robots in the book. This device can be repro-
grammed over and over because it uses flash read-only memory
for program storage. This makes it ideal for experimenting because
the chip does not need to be erased with an ultraviolet light source
every time you need to tweak the code or try something new.

The PIC 16F84 is an 18-pin device with an 8-bit data bus and reg-
isters. We will be using a 4-MHz crystal for the clock speed. This
is very fast for our application when you consider that it is run-

FIGURE 3.1
Pinout of the PIC 16F84
microcontroller.

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