1. Lecture 6: TI MSP430 IO Interfacing
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 = mA
VF = V

6. ECE 447: LED

7. ECE 447: LED Interfacing VDD=3 V R=? VDD – VF – VOL Forward current
I ≈ IF VF
Forward voltage
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 VF
Forward voltage
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. 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
74HC245
DIR OE
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
MSP430
Port 1
Port 2
74HC245
DIR OE
74HC245
DIR OE
I/O device 1
I/O device 8

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

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

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