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ECE 447 Fall 2009

ECE 447 Fall 2009. Lecture 6: TI MSP430 IO Interfacing. Agenda. Internal/External Resistors LEDs Switch Debouncing Buffers Port Multiplexing. ECE 447: MSP430 Current Limits. V DD = 3 V. Maximum sink current. V OHmin = 2.4 V. I OLmax = 40 mA. Maximum source current.

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ECE 447 Fall 2009

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  1. ECE 447 Fall 2009 Lecture 6: TI MSP430 IO Interfacing

  2. Agenda • Internal/External Resistors • LEDs • Switch Debouncing • Buffers • Port Multiplexing

  3. ECE 447: MSP430 Current Limits VDD= 3 V Maximum sink current VOHmin= 2.4 V IOLmax = 40 mA Maximum source current IOHmax= 40 mA VOLmax= 0.6 V GND=0 V

  4. Internal Pull Up Resistor

  5. ECE 447: Light Emitting Diode (LED) + Forward current Forward voltage IF VF – Typical values for common LEDs IF = 10-20 mA VF = 1.7-2.4 V

  6. ECE 447: LED

  7. ECE 447: LED Interfacing VDD=3 V R=? VDD – VF – VOL Forward current VF Forward voltage I ≈ IF VOL Low Level Output Voltage VOL Low Level Output Current (sink current) IOL buffer I ≈ IF  IOLmax R ≈ (VDD – VF – VOL) / IF

  8. ECE 447: LED Interfacing VDD=3 V R1=? VDD – VF – VCE Forward current I ≈ IF Forward voltage VF VCE Collector-Emitter Voltage R2=? ICE Collector-Emitter Current I ≈ IF ICEmax IOH IOHmax VBE R1≈ (VDD – VF – VCE) / IF R2 (VOH – VBE) / IOHmax Base-Emitter Voltage

  9. ECE 447: MAN-72: 7-Segment LED

  10. ECE 447: Single Switch/Push Button

  11. ECE 447: Switch Key Bouncing key bounce, tBOUNCE key bounce, tBOUNCE typically, tBOUNCE < 10 ms

  12. ECE 447: Key Debounce in Software key bounce, tBOUNCE key bounce, tBOUNCE typically, tBOUNCE < 10 ms debouncing delay debouncing delay update display

  13. ECE 447: Key Debounce in Hardware

  14. Schmidt Trigger Debounce

  15. Schmidt Trigger Performance

  16. OE 74HC245 DIR MSP430 and Compatible Logic Devices • HCT Family • Uses CMOS technology but TTL (Transistor-transistor logic) input logic levels • Slower performance than HC, replaces TTL • HC Family • High performance CMOS Logic chips • Combines strengths of TTL with CMOS • Can operate at lower voltages (i.e. 3V) Data In Data Out

  17. ECE 447: Octal Buffer 74HC245 Note: All 8 outputs controlled by one enable, OE

  18. ECE 447: Octal Buffer 74HC244 Note: Outputs controlled by two enables, 1OE & 2OE (1OE controls 1A0-1A3, 2OE controls 2A0-2A3)

  19. ECE447: Latches 74HC373

  20. ECE447: Registers 74HC374

  21. ECE 447: Port Multiplexing Allow multiple devices to share the input and output ports of the microcontroller. Additional hardware typically needed to support connection and selection of peripheral devices. Software typically selects the peripheral devices using additional output pins. Some I/O devices have built-in enable signals.

  22. ECE 447: Port Multiplexing OE OE 74HC245 74HC245 DIR DIR MSP430 Port 2 Port 1 . . . . . . . . . . . . I/O device 1 I/O device 8 . . . . . . .

  23. ECE 447: Port Multiplexing OE MSP430 Port 2 Port 1 8 1G 2G 74HC245 74HC244 DIR I/O device 2 (e.g., keypad) I/O device 1 (e.g., LCD display)

  24. OE ECE 447: Port Multiplexing MSP430 Port 2 Port 1 8 OE CP 74HC245 74HC373 DIR I/O device 2 (e.g., 7 segment display) I/O device 1 (e.g., LCD display)

  25. Summary • Internal/External Resistors • LEDs • Switch Debouncing • Buffers • Port Multiplexing

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