Page 475 - Robot Builder's Bonanza

444 UNDERSTANDING MICROCONTROLLERS

tions make efficient use of data space. As long as you follow good coding practice, you should
seldom run out of data storage space.

ERASING AND STARTING OVER
As noted, most microcontrollers are meant to be programmed over and over again. Each time
you download a program to it, the old one is erased, and the new one takes its place. The
most common program storage used in modern microcontroller is flash, the same as that used
in USB thumb drives, or the CompactFlash cards in a digital camera.
There is an exception to completely erasing the flash memory
each time you download a new program. Some micro-
G controllers are set up to allow a special “bootloader” area in
flash, which contains special setup code to make it easier to
reprogram the chip without having to pull it out of its circuit.

IN- FIELD PROGRAMMING (AND REPROGRAMMING)
A key benefit of microcontrollers with flash memory is that they can be programmed and
reprogrammed “in circuit”—that is, while the chip is still plugged into whatever circuit board
home it’s living in.
This has enormous potential for use in your programmable robot. With in- field program-
ming there is no need to remove the microcontroller chip from its circuit in your robot to
reprogram it. Instead, you merely connect a cable from your PC and download the new pro-
gram. Of course, this requires that the microcontroller have an onboard connector so it can
be attached to your PC cable.

ONE- TIME PROGRAMMABLE

Less costly microcontrollers are made to be programmed only once, and are intended for
permanent installations. These one- time programmable (OTP) microcontrollers are popular
in consumer goods and automotive applications.
For robotics applications, the OTP is useful for dedicated processes, such as controlling
servos or triggering and detecting a sonar ping from an ultrasonic distance measurement
system. You’ll find a number of the ready- made hobby robotic solutions on the market today
that have, at their heart, an OTP microcontroller. The microcontroller takes the place of more
complex circuitry that uses individual integrated circuits.

Microcontroller Programmers

All microcontrollers need to be programmed. The complexity of the programming setup
depends on the architecture of the microcontroller. For example, the PICAXE and BASIC
Stamp controllers can be connected to a PC using a simple cable— typically just a serial cable
that has the usual DB- 9 connector on one end (for connection to the PC) and header pins on
the other (for connection to the controller).
Chip- only microcontrollers without a built- in language need a programmer, a physical
device that provides all the necessary power and signal connections to the chip. The program-

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