Page 76 - DCAP210_INTRODUCTION__TO_MICROPROCESSORS

Introduction to Microprocessors

Notes microcontroller leaves its normal flow of execution and jumps directly to the interrupt service routine.
Interrupts can in general be nested such that a new interrupt can suspend the execution of another
interrupt. Most microcontrollers have at least one, though some have several interrupt sources.
5.3.7 Brown-out Detector

Brown-out detectors are also common in many microcontrollers and they reset a microcontroller
if the supply voltage falls below a nominal value. Brown-out detectors are usually employed to
prevent unpredictable operation at low voltages, especially to protect the contents of EEPROM
type memories.

5.3.8 Analogue-to-Digital Converter
Some microcontrollers are equipped with analogue-to-digital converter circuits. Usually these
converters are 8 bits, but some microcontrollers have 10- or even 12-bit converters. A/D converters
usually generate interrupts when a conversion is complete so that the user program can read the
converted data very quickly. A/D converters are very useful in control and monitoring applications
since most sensors produce analogue output voltages.

5.3.9 Serial Input/Output

Some microcontrollers contain hardware to implement a serial asynchronous communications
interface. The baud rate and the data format can usually be selected in software. If serial input/
output hardware is not provided, it is easy to develop software to implement serial data transfer
using any I/O pin of a microcontroller. Some microcontrollers incorporate SPI (Serial Peripheral
Interface) or IC (Integrated InterConnect) bus interfaces. These enable a microcontroller to interface
to other compatible devices easily.

5.3.10 EEPROM Data Memory
EEPROM type memory is also very common in many microcontrollers. The programmer can
store non-volatile data in such memory and can also change this data whenever required. Some
microcontroller types provide between 64 and 256 bytes of EEPROM data memories, while some
others do not have any such memories.

5.3.11 LCD Drivers
LCD drivers enable a microcontroller to be connected to an external LCD display directly. These
drivers are not very common since most of the functions provided by them can be implemented
by software.

5.3.12 Analogue Comparator

Analogue comparators enable analogue signals to be compared easily. These circuits are not very
common and are only implemented in some microcontrollers.

5.3.13 Real-time Clock

The real-time clock is another feature which is implemented in some microcontrollers. These
microcontrollers usually keep the date and time of day and they are intended for the consumer
market

5.3.14 Sleep Mode
Some microcontrollers (e.g. PIC) offer sleep modes where executing this instruction puts the
microcontroller into a mode where the internal oscillator is stopped and the power consumption

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