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 GND=0 V V DD = 3 V Maximum sink current I OLmax = 40 mA V OLmax = 0.6 V V OHmin = 2.4 V Maximum source current I OHmax = 40 mA

4. Internal Pull Up Resistor

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

6. ECE 447: LED

7. ECE 447: LED Interfacing V DD =3 V I ≈ I F Forward current Forward voltageVFVF V OL buffer Low Level Output Voltage I OL Low Level Output Current (sink current) R=? R ≈ (V DD – V F – V OL ) / I F I ≈ I F  I OLmax V OL V DD – V F – V OL

8. ECE 447: LED Interfacing V DD =3 V I ≈ I F Forward current Forward voltage VFVF V CE Collector-Emitter Voltage I CE Collector-Emitter Current R 1 =? R 1 ≈ (V DD – V F – V CE ) / I F R 2  (V OH – V BE ) / I OHmax R 2 =? V BE Base-Emitter Voltage V DD – V F – V CE I ≈ I F  I CEmax I OH  I OHmax

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

10. ECE 447: Single Switch/Push Button

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

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

13. ECE 447: Key Debounce in Hardware

14. Schmidt Trigger Debounce

15. Schmidt Trigger Performance

16. 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) 74HC245 DIR OE 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 1A 0 -1A 3, 2OE controls 2A 0 -2A 3 )

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 Port 2 Port 1 I/O device 1 74HC245 DIR OE I/O device 8 74HC245 DIR OE............ MSP430

23. ECE 447: Port Multiplexing Port 2 Port 1 I/O device 1 (e.g., LCD display) I/O device 2 (e.g., keypad) 74HC24574HC244 DIR OE 1G 8 2G MSP430

24. Port 2 Port 1 I/O device 1 (e.g., LCD display) I/O device 2 (e.g., 7 segment display) 74HC24574HC373 DIR OE 8 CP MSP430 ECE 447: Port Multiplexing

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