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Basic Interfacing
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  1. Basic Interfacing ECET 2210

  2. Overview • IC Drive Capability • LED Interfacing • Schmitt Triggered Inputs • Switch Interfacing • Switch Debouncing • Clock Generators • Power-On-Reset

  3. Digital Digital Digital Drive Capability High Output IOH IIH Low Output IIH

  4. Digital Digital Digital Drive Capability High Output IOL IIL Low Output IIL

  5. LED Interfacing Probably not. Will this work? 10 - 20 mA

  6. LED Interfacing VCC 10 - 20 mA • Sinking generally provides more drive capability than sourcing • Always refer to specification sheets

  7. Schmitt Triggered Inputs Waveform Thresholds Crossings First Crossings Final Waveform

  8. Schmitt Triggered Inputs Waveform Thresholds Crossings First Crossings Final Waveform

  9. Schmitt Triggered Inputs Waveform Thresholds Crossings First Crossings Final Waveform

  10. Schmitt Triggered Inputs Waveform Thresholds Crossings First Crossings Final Waveform

  11. Schmitt Triggered Inputs Waveform Thresholds Crossings First Crossings Final Waveform

  12. Push Button Rocker Lever Slide Rotary Toggle Switch Terminology Types Mechanisms Construction

  13. Switch Terminology Types • Fixed Mechanisms • Momentary Construction

  14. Switch Terminology Types Mechanisms Construction Single-pole Single-throw (SPST) Poles are Pivots Throws are the number of possible contacts the arm can touch

  15. Switch Terminology Types Single-pole Single-throw (SPST) Mechanisms Construction Single-pole Double-throw (SPDT) Double-pole Single-throw (DPST) Double-pole Double-throw (DPDT)

  16. Switch Interfacing Will this work? NO - Inputs float in open position Can pick up noise Can damage CMOS

  17. Switch Interfacing Will this work? VCC NO - Inputs float during transition

  18. Switch Interfacing Will this work? YES - open provides high input VCC closed provides low input

  19. Switch Bounce VCC Switch Bounce

  20. Switch Bounce VCC

  21. Switch Bounce Reset VCC Glitch caused by bounce Typically 50-100 ms

  22. Debouncing a Single Throw Switch One-Shot Schmitt Trigger Pulse > 100 ms VCC One-Shot Retriggerable or Non-Retriggerable?

  23. Typical values 33 kW 4.7 mF Debouncing a Single Throw Switch One-Shot Schmitt Trigger VCC Similar to POR

  24. Set Q Reset Debouncing a Double Throw Switch Set VCC Transition Reset VCC

  25. Set Q Reset Debouncing a Double Throw Switch Set VCC Transition Reset VCC

  26. Set Q Reset Debouncing a Double Throw Switch Set VCC Transition Reset VCC

  27. Set Q Reset Debouncing a Double Throw Switch Set VCC Transition Reset VCC

  28. Clock Generators 555 Timer Schmitt Trigger Oscillator

  29. Clock Generators 555 Timer The most common low-frequency clock generator Schmitt Trigger Advantages: Oscillator • easily obtainable • easy setup • adjustable duty cycle Disadvantages: • limited frequency (£ 100 kHz) • less stable frequency • less accurate frequency

  30. Clock Generators 555 Timer Schmitt Trigger Oscillator

  31. Clock Generators 555 Timer Advantages: • easily obtainable Schmitt Trigger • easy setup Oscillator Disadvantages: • limited frequency • not for precision applications • very dependent on technology

  32. Clock Generators 555 Timer Prepackaged clock generator requires only power and ground connections Schmitt Trigger Advantages: Oscillator • easily setup • very precise frequency • very stable frequency Disadvantages: • more expensive • primarily available ³ 1 MHz

  33. Power-On-Reset What is the problem with this circuit when power is applied?

  34. Power-On-Reset What is the problem with this circuit when power is applied? Initial State? Can we insure that the initial state will always be the same?

  35. Power-On-Reset The circuit:

  36. Vout Vc t+ to to Power-On-Reset The circuit:

  37. Power-On-Reset Advantages: • Initializes storage devices to a known state (i.e. counters, flip-flops, etc.) • Provides time for power supply to stabilize

  38. Power-On-Reset Advantages: • Initializes storage devices to a known state (i.e. counters, flip-flops, etc.) • Provides time for power supply to stabilize

  39. Power-On-Reset Example Solution:

  40. Basic Interfacing