Download presentation
Presentation is loading. Please wait.
Published byErik Perry Modified over 9 years ago
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
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.