1. Principles & Applications
Digital Electronics
Principles & Applications
Fifth Edition
Roger L. Tokheim
Chapter 12
Digital Systems
© Glencoe/McGraw-Hill

2. CHAPTER 12 PREVIEW Elements of a System Computer Organization
Computer Peripheral Devices
MPU Based System
Digital Clock
Multiplexing Displays
Simplified Frequency Counter
Serial/Parallel Data Transmission
Digital Timer
Digital Games (Dice and Roulette)
Programmable Logic Controller
Microcontrollers

3. ELEMENTS OF A SYSTEM
Control
Input
Storage
Processing
Output

4. COMPUTER ORGANIZATION - CLASSICAL
Memory
Output
Input
Arithmetic
and Logic
Control

5. COMPUTER PERIPHERAL DEVICES
Modem
Fax
Keyboard
Mouse
Joystick
Paddles
Graphics tablet
Microphone
Light pen
Scanner
Bar code reader
Strip reader
Various Sensors
CPU and
Internal Memory
Output
Input
Input/Output
Storage
Monitor
(CRT or LCD)
Television
Printer
Speaker
Plotter
Floppy disk drive
Hard disk drive
Optical disk drive
Tape unit

6. Microcomputer system block diagram
Input
ports
The input ports connect to devices such as keyboards
The address bus
is unidirectional
The data bus
is bidirectional
MPU
The MPU is the heart of the system
ROM
The ROM contains programs and permanent data
The control bus
is unidirectional
RAM
The RAM contains temporary data (and programs)
Output
ports
The output ports connect to devices such as printers

7. signal on the control bus 3. The addressed port putsIN
Reading input data
Input
ports
2. The MPU asserts a READ
signal on the control bus
1. The MPU places an input
address on the bus
3. The addressed port puts
its data on the bus
4. The data is stored
in the MPU
MPU
MPU
ROM
RAM
Output
ports

8. signal on the control bus 1. The MPU places an output
Writing output data
Input
ports
2. The MPU asserts a WRITE
signal on the control bus
1. The MPU places an output
address on the bus
3. The MPU places the
data on the bus
MPU
ROM
4. The data is written
to the output port
Output
ports
RAM
Output
ports
OUT

9. DIGITAL CLOCK Hours Minutes Seconds Decoder/driver Decoder/driver
1 pph
1 ppm
Mod 12 counter
Mod 60 counter
Mod 60 counter
1 Hz
1 pps
DIGITAL CLOCK
60 Hz
 60

10. MULTIPLEXED DISPLAYS a 8 b BCD- 4 c 7-seg driver 2 d e 1 f g
Digit drivers

11. 11 cycles are counted (fX = 11 Hz)
A basic digital
frequency counter
Start/stop
Counters/decoders/drivers fX fX
Start/stop
1 second {
11 cycles are counted (fX = 11 Hz)

12. SERIAL/PARALLEL DATA CONVERSION
Shift registers can be used to convert from serial-to-parallel or the reverse from parallel-to-serial.
Serial in
Parallel out
Parallel in
Parallel out
Serial in
Serial out
Serial out
Parallel in

13. Serial data transmission
A UART receives bytes from the data bus and transmits them one bit at a time.
UART
Receiver
RS232
Driver
Start bit
Stop Bit
Bit 6
Bit 4
Bit 1
Bit 2
Bit 3
Bit 7
Bit 5
Bit 0
To modem
Transmitter
Serial data transmission
is relatively slow!
Control

14. Parallel data transmission is relatively fast!
Here, the UART assembles bits from the serial port
and places them on the data bus one byte at a time.
UART
RS232 to
Logic
Level
Receiver
Transmitter
From modem
Parallel data
transmission
is relatively fast!
Control

15. DIGITAL TIMER Clock (time base) Input controls Self-stopping
Down counter
Latch/Decoder
Driver
Magnitude
comparator
Alarm

16. DIGITAL DICE GAMES Roll Dice +5V Roll Dice +5V Counter Decoder/ Clock
Mod-6
Decoder/
Driver
+5V
Roll Dice
Clock
Counter
Mod-6
Logic Block
+5V

17. DIGITAL ROULETTE GAME +5V Audio Amplifier Power-up Initializing
Circuit
Spin
Wheel
input
+5V
Voltage
Controlled
Oscillator
(VCO)
Ring Counter
(shift register)
Simulated
Roulette
Display

18. PROGRAMMABLE LOGIC CONTROLLERS
PLCs are heavy-duty computer systems used for machine control.
PLCs must be rugged to withstand the rigors of a chemical, warehouse/storage, or assembly line environment.
PLCs use MODULAR organization.
Power Supply
Programming Module
Memory
Processing
Module
CPU
Output
Input
Input Sensors
- pressure
- mechanical
- optical
A/D converters
Motors
Solenoids
Pneumatic devices
D/A converters

19. MICROCONTROLLERS
A microcontroller is considered a “computer on a chip.”
A microcontroller IC contains a CPU, RAM, ROM or EEPROM, a clock, and input/output capabilities.
Microcontrollers are:
Very inexpensive
Commonly preprogrammed and embedded in products
Commonly used to perform control functions
Manufactured in huge quantities
NOT used as the CPU in general purpose computers
Microcontroller-based systems have much less semiconductor memory (RAM, EEPROM), cost less, use less printed circuit board space, and perform fewer commands than microprocessor based systems.