Logic Compatibility - Introduction to Microprocessor Systems - Lecture Sli, Lecture notes of Computer Science

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Topics

• Logic Compatibility

• Microprocessor peripherals

– Timers

• Periodic
• Watchdog
• Real-time
• ADuC7026 timers

– Pulse-width modulators (PWM)

– Direct memory access (DMA)

FET Basics

• Field effect transistors (FETs) are used as the switching

elements in logic gates

• When turned on, the FET presents a very low impedance to current, like a closed switch
• When turned off, the FET presents a very high impedance to current, like an open switch
• There are two ways to construct a FET
• N-channel P-channel

Logic Family Characteristics

• Voltage

• V (^) IHmin – minimum input voltage recognized as a logical 1
• V (^) ILmax – maximum input voltage recognized as a logical 0
• VOHmin – minimum voltage output for a logical 1
• VOLmax – maximum voltage output for a logical 0

• Current

• Currents are defined positive in, negative out
• I (^) OHmax – maximum output current sourced for a logical 1
• I (^) OLmax – maximum output current sunk for a logical 0
• I (^) IHmax – maximum input current required at a logical 1
• I (^) ILmax – maximum input current required at a logical 0
• I (^) OZH, I (^) OZL – current drawn/sourced when tri-stated

• Logic families Docsity.com

Simple Circuit Models

• Drivers

• Receivers

Logic Compatibility

• Static (DC) Compatibility

• Voltage
• Current
• Overvoltage tolerant inputs

• Dynamic compatibility

• Capacitive loading, mutual induction, reflections, etc.

• Exercises

Timer Peripherals

• Timer/counter modules used to

– Generate signals with specified frequency / duty

cycle

– Count external events, measure pulse width

– Generate absolute delays, periodic interrupts

• Building a timer peripheral

– Basic free-running timer

– Periodic timer enhancements

– Clock selection and prescaling

– Adding capture capability

A Periodic Timer

Clock Selection and Prescaling

Real-Time Clocks (RTCs)

• RTCs provide microprocessor systems with

absolute time information

– Absolute time does not necessarily mean

calendar/clock time

– Typically operate from 32.768KHz crystal with

battery or capacitor back-up power supply

– Generate periodic interrupts

– Often contain a small amount of RAM –

historically this was where the PC stored its

configuration (BIOS) settings since it was non-

volatile.

• Dallas Semiconductor DS1375 Docsity.com

Watchdog Timers

• Watchdog timers are used to guard a system

against lock-up due to software errors or soft

failures in hardware

– Often included in microcontrollers and CPU

supervisor circuits.

• Retriggering is usually done in the main

program loop

• Watchdog output can be used to reset the CPU

or as a nonmaskable interrupt (NMI)

• Maxim MAX6323/MAX6324 Docsity.com

ADuC7026 Timers

• Timer

• General-purpose timer
  • 32-bit counter
  • Multiple clock sources with prescaler
  • Capture register
  • Binary or H:M:S formats

ADuC7026 Timers

• Timer

• Wake-up timer
  • 32-bit counter
  • Can run on 32kHz clocks
  • Binary or H:M:S format

Timer3 Secure Clear Mode

PWM Peripherals

• A basic pulse-width modulator peripheral creates a

rectangular wave whose duty cycle can be controlled

• PWM allows us to control the average power delivered to a

load without changing the voltage supplied to it

• The ADuC7026 contains a very capable 3-phase PWM

that is intended to do motor control