DM164120-2 Microchip Technology, DM164120-2 Datasheet - Page 27

• Manufacturer Part Number: DM164120-2
• Description: BOARD DEMO PICKIT 2 44PIN
• Manufacturer: Microchip Technology
• Type: MCUr

Specifications of DM164120-2

• Contents: 3 Boards (1 Populated, 2 Bare)
• Processor To Be Evaluated: PIC16F
• Silicon Manufacturer: Microchip
• Kit Contents: PIC16F Device, 2 PCB Boards
• Features: Small Surface Mount Prototype Area, Two Bare PCB Boards
• Development Tool Type: Hardware - Daughter Card
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With/related Products: PIC16F887
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

© 2007 Microchip Technology Inc.
3.2.6
Mechanical switches play an important and extensive role in practically every com-
puter, microprocessor and microcontroller application. Mechanical switches are inex-
pensive, simple and reliable. However, switches can be very noisy electrically. The
apparent noise is caused by the closing and opening action that seldom results in a
clean electrical transition. The connection makes and breaks several, perhaps even
hundreds, of times before the final switch state settles.
The problem is known as switch bounce. Some of the intermittent activity is due to the
switch contacts actually bouncing off each other. Imagine slapping two billiard balls
together. The hard non-resilient material doesn’t absorb the kinetic energy of motion.
Instead, the energy dissipates over time and friction in the bouncing action against the
forces push the billiard balls together. Hard metal switch contacts react in much the
same way. Also, switch contacts are not perfectly smooth. As the contacts move
against each other, the imperfections and impurities on the surfaces cause the electri-
cal connection to be interrupted. The result is switch bounce.
The consequences of uncorrected switch bounce can range from being just annoying
to catastrophic. For example, imagine advancing the TV channel, but instead of getting
the next channel, the selection skips one or two. This is a situation a designer should
strive to avoid.
Switch bounce has been a problem even before the earliest computers. The classic
solution involved filtering, such as through a resistor-capacitor circuit, or through re-set-
table shift registers (see Figure 3-4 and Figure 3-5). These methods are still effective
but they involve additional cost in material, installation and board real estate. Debounc-
ing in software eliminates these additional costs.
FIGURE 3-4:
FIGURE 3-5:
Lesson 6: Switch Debouncing
SW
SW
FILTERING DEBOUNCE SOLUTION
SHIFT REGISTER DEBOUNCE SOLUTION
Debounce
Clock
+V
R1
R1
44-Pin Demo Board Lessons
+V
D
CLK
R2
C
CLR
1
Filtered
Switch
Output
Qn
Filtered
Switch
Output
DS41296B-page 23