Principles & Applications Digital Electronics Principles & Applications Fifth Edition Roger L. Tokheim Chapter 12 Digital Systems ©1999 Glencoe/McGraw-Hill

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

ELEMENTS OF A SYSTEM Control Input Storage Processing Output

COMPUTER ORGANIZATION - CLASSICAL Memory Output Input Arithmetic and Logic Control

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

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

signal on the control bus 3. The addressed port puts IN 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

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

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

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

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)

SERIAL/PARALLEL DATA CONVERSION Shift registers can be used to convert from serial-to-parallel or the reverse from parallel-to-serial. 1 0 1 0 1 1 1 1 Serial in Parallel out 1 0 1 0 1 1 1 1 Parallel in Parallel out 1 0 1 0 1 1 1 1 Serial in Serial out 1 0 1 0 1 1 1 1 Serial out Parallel in

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

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 01101110 Transmitter From modem Parallel data transmission is relatively fast! Control

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

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

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

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

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.