428 Computer Architecture and Organization
embedded system, we may consider an audio alarm system for educational institutions, which is capable
of automatically turning on and off several heavy-duty electric bells at prede ned times. This real-time
embedded system would need a solid-state relay along with some display and keys arranged around a
microcontroller, like ATmega8.
POINTS TO REMEMBER
R Modern embedded system design focuses on selection of proper microcontroller from a vast range
of these available in the market. External interfacings with these microcontrollers are maintained to
a minimum level and generally external program or data memory is not considered as a good design
practice.
R Before the device selection for embedded system design, architectural features of all available
microcontrollers in the market are expected to be studied by the system designer.
QUICKSAND CORNER
Any embedded system designer should remember
that gone are those days of external memory inter-
facing with any microcontroller. For an ef cient
and optimum design, the designer must have ade-
quate knowledge of overall architecture regarding
all major microcontrollers available. If the system
has to be battery-powered, then additional care is
needed.
Designing any microprocessor based system
is easier as all of its support devices are to be
externally interfaced, which offers more exibil-
ity in device selection and in the design decisions.
This exibility is not present in embedded system
design and the controller selection plays the piv-
otal role in nal success of the designed unit in the
commercial market.
REVIEW QUESTIONS
Target the Correct Option
1. Which one of the following is not an embed-
ded system?
(a) Laptop (c) PC keyboard
(b) Mobile handset (d) None of these
2. The microcontroller ADμc812 belongs to
(a) Intel (c) Hitachi
(b) Motorola (d) none of these
3. Which one of the following is not included
within the architecture of any microcontroller?
(a) Timer (c) Stepper motor
(b) USART (d) None of these
4. How many pins are there in ATmega8 DIP?
(a) 24 (c) 40
(b) 28 (d) none of these
5. Which of the following architectural feature
is not available in ATmega8 microcontroller?
(a) On-chip ADC (c) On-chip oscillator
(b) On-chip DAC (d) None of these
6. The address of 8K bytes of Flash of ATmega8
varies from 0000H to
(a) 0FFFH (c) FFFFH
(b) 1FFFH (d) none of these
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Embedded Systems 429
Find in Few Seconds
7. If the initial value of the stack pointer of
ATmega8 is 00FFH, then after a PUSH opera-
tion, its value would be
(a) 0100H (c) 00FEH
(b) 00FFH (d) none of these
8. The number of sleep modes offered by
ATmega8 for ef cient power management is
(a) 7 (c) 2
(b) 4 (d) none of these
9. With respect to the current sourcing capacity
of any port pin of ATmega8, its current sink-
ing capacity is
(a) less (c) more
(b) same (d) none of these
10. The number of pins of Renesas microcon-
trollers varies from
(a) 20 to 500 (c) 40 to 48
(b) 28 to 64 (d) none of these
1. What is the difference between a battery-
operated embedded system and a battery
backed-up embedded system?
2. In which way the processing power may clas-
sify embedded systems?
3. What is the difference between a real-time
system and a non-real-time system?
4. In how many ways ATmega8 may be reset?
5. What is the function of a watch-dog timer?
6. Why the 8K bytes of Flash of ATmega8 is
divided into two blocks?
7. What is the purpose of providing EEPROM
in ATmega8?
8. What is meant by brown-out reset?
9. What is meant by design issues in embedded
system design? Make a list of them.
10. Which type of embedded system is expected
to be robust in design? Why?
Spend Some Time Here
1. Why embedded systems are not capable of
executing user’s application program?
2. Try to nd out a few more attributes to clas-
sify embedded systems other than those pre-
sented through Figure 14.1.
3. Why AVR microcontrollers offer three types
of memory blocks?
4. Why external memory interfacing is undesir-
able for embedded systems?
5. What is indicated by the term core of a
microcontroller?
6. What is the advantage of brown-out reset of
ATmega8?
7. What is the difference between power-on
reset and external reset of ATmega8?
8. What is the advantage of having an on-chip
oscillator within a microcontroller?
9. What are the advantages of Renesas micro-
controllers?
10. What modi cations are necessary in the
design of the system, shown in Figure 14.11 ,
so that many different patterns audio alarm
(sound characteristics, like: siren, gong, ute,
etc.) can be accommodated by the system?
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