Page 181 - Programming Microcontrollers in C

166 Chapter 4 Small 8-Bit Systems

compile individually and examine if they create outlandish code. Once
these small functions are all debugged, you can integrate them into
your program as either inline code or as function calls. Hence, the
fundamental rule of writing good high-level code for a
microcontroller: the production of good C code for a microcontroller
is a joint effort between the programmer and the compiler writer.
Erasure of EEPROM causes component wear, and most EEPROMs
will wear out after a large number of erasures. The nature of the deg­
radation is that the component refuses to erase after many erasures.
There has been no evidence that data retention is affected by repeated
erasures. The number of erasures that can cause problems is tempera­
ture sensitive. Most of these devices are rated for 10,000 write/erase
cycles at the maximum rated temperature for the part. At room tem­
perature, the number of write/erase cycles without damage can grow
to several hundred thousand. In light of these facts, it is important that
programs use care in rewriting the contents of EEPROM.

EXERCISES
1. The EEPROM in microcontrollers erase to the 1 state. Write a
function that checks to determine if an erasure cycle erases the
contents of a given location in memory.

2. Write a function that compares data to be programmed into
EEPROM and determine if it is necessary to erase a byte contain­
ing data before it is reprogrammed. This approach will extend the
life of the EEPROM.

Timers

The systems of timers placed on microcontrollers are among the
most creative engineering efforts most people will ever see. The func­
tions of these timers cover literally dozens of different operations.
This set of peripheral components mainly relieve the computer of
much work associated with execution of the peripheral function. We
will start with the simplest timer and outline different timer capabili­
ties in increasing complexity. The most basic timer in the M68HC05
family is called the 15-bit timer, and probably the most advanced
timer system is the 16-bit timer. These different timer systems are
literally unrelated in the features they offer. Another timer feature