AN60024 PSoC 3, PSoC 4, PSoC 5LP Switch Debouncer and Glitch Filter.pdf

AN60024
Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Author: Mark Ainsworth
Associated Project: Yes
Associated Part Family: CY8C3xxx, CY8C42xx, CY8C5xxxLP
Software Version: PSoC Creator™ 3.0 and higher
Related Application Notes: For a complete list of the application notes, click here.
To get the latest version of this application note, or the associated project file, please visit
http://www.cypress.com/go/AN60024.
AN60024 introduces the concepts of switch debouncing and glitch filtering for digital input signals, and shows how to
®
create several debounce and filter solutions for PSoC 3, PSoC 4, and PSoC 5LP, using PSoC Creator™.
and dynamically adapt to different switch or button
characteristics.
Contents
Introduction .......................................................................1
Universal Digital Blocks (UDBs) ...................................2
I/O Pin Setup .....................................................................3
A Switch Bounce-Sensitive Design ...................................4
Switch Debouncing by Sampling .......................................6
Switch Debouncing Using Software ..................................6
Switch Debouncing Using Hardware ............................... 10
Debouncer Component .............................................. 10
Glitch Filtering ................................................................. 11
Summary ......................................................................... 12
Design Projects ............................................................... 13
Related Application Notes ............................................... 13
Worldwide Sales and Design Support ............................. 15
Figure 1. Scope Shot Showing Switch Bounce on
Transition from High to Low Voltage
Introduction
®
®
CapSense
and TrueTouch
notwithstanding, many
products still have mechanical buttons or switches. When
a switch is pressed or released, its output can oscillate for
a brief period, as Figure 1 shows.
In some applications, these oscillations may cause other
parts of the system, such as the CPU, to falsely detect
multiple press and release events. This in turn can cause
erratic and unexpected system behavior. Imagine what
might happen if, for example, the switch is the „Speed Up‟
button on a treadmill.
Filtering out these oscillations is known as switch
debouncing. You could use a simple RC filter, but why pay
for extra components when PSoC devices can do the job
easily and in many ways, using minimal device resources?
And, an RC filter is fixed, while with PSoC you can easily
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This application note shows several ways to take
advantage of the flexibility of PSoC. With PSoC, switch
debouncing can be done using hardware, software, or
both. Glitch filtering, which is similar to switch debouncing,
is also demonstrated.
You will also see how fast and easy it is to use PSoC
Creator to produce many different designs. Several PSoC
Creator demonstration projects are attached to this
application note. They are designed to work with the
CY8CKIT-001 PSoC Development Kit, but can be easily
adapted to work with most other kits.
Document No. 001-60024 Rev. *O
1
Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
This application note assumes that you have some basic familiarity with PSoC 3, PSoC 4 or PSoC 5LP devices and the PSoC
Creator IDE. If you are new to PSoC, you can find introductions in the following application notes:



AN54181, Getting Started with PSoC 3
AN77759, Getting Started with PSoC 5LP
AN79953, Getting Started with PSoC 4
If you are new to PSoC Creator, see the PSoC Creator home page.
Universal Digital Blocks (UDBs)
Many of the designs shown in this application note make use of the Universal Digital Blocks (UDBs) available in PSoC.
A PSoC device has as many as 24 UDBs. Each UDB contains:



two small programmable logic devices (PLDs),
a datapath module containing a programmable 8-bit ALU,
and other registers and functions, as Figure 2 shows.
Figure 2. UDB Block Diagram
PLD
Chaining
PLD
12C4
(8 PTs)
PLD
12C4
(8 PTs)
Clock
and Reset
Control
Status and
Control
Datapath
Datapath
Chaining
Routing Channel
UDBs, as well as PSoC‟s Digital System Interconnect (DSI) routing fabric, give you the flexibility to design complex custom
peripheral functions. This allows you to optimize your design at the system level as well as significantly reduce CPU usage.
For more information on UDBs and PSoC digital design in general, see the following application notes:



AN81623, PSoC Digital Design Best Practices
AN82250, PSoC Implementing Programmable Designs with Verilog
AN82156, PSoC Designing PSoC Creator Components with UDB Datapaths
The PSoC Creator IDE offers an extensive library of preprogrammed peripherals. It also enables you to create your own
custom designs.
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
I/O Pin Setup
Before we look at switch debouncing, it may be helpful to review how best to connect a switch or button to a PSoC I/O pin. A
button typically shorts to ground when pressed and opens when released. To get valid digital high voltages, a pull-up resistor
is required, as the leftmost diagram in Figure 3 shows.
Each PSoC I/O pin has an internal pull-up resistor. With PSoC Creator, you can use the Digital Input Pin Component to enable
the pull-up; Figure 3 also shows some example PSoC Creator schematics.
Figure 3. Grounded Switch Circuit and Corresponding Example PSoC Creator Schematics
Vddio
PSoC 3/4/5LP
You can read the pin value using firmware or hardware. The pin value is logic „0‟ when the switch is pressed, and logic „1‟
when released. If you want to reverse the polarity, you can do the inversion in firmware or in hardware. In hardware just add
an inverter, as the rightmost schematic in Figure 3 shows.
After placing the Pin Component on your PSoC Creator project schematic, double-click the Component to configure it. A
configuration dialog is displayed, as Figure 4 shows.
Enter a name for the Pin; in this case it is “SW”, for “switch”. Select the options on the Type and General tabs. Checking the
HW Connection and Show External Terminal boxes is optional, depending on your application. To enable the pull-up
resistor, set the Drive Mode to Resistive Pull Up, and the Initial State to High (1). For more information, see the Pins
Component datasheet.
Figure 4. Digital Input Pin Component Configuration
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
A Switch Bounce-Sensitive Design
Figure 5 shows a poor design – it is sensitive to switch bounce.
Figure 5. Schematic Showing a Design that is Overly Sensitive to Switch Bounce
The positive and negative edges from the input pin are captured by two digital flip flops (DFF) and trigger an interrupt. Code 1
on page 5 shows how to handle the interrupt. The interrupt handler code does the following:

Resets the DFFs by writing to the Control Reg Component „SwReset‟. The Component is configured in pulse mode;
writing a „1‟ to it generates a single pulse that resets the DFFs.

Increments a global „count‟ variable
The loop in main() continually displays the value of „count‟ on the LCD.
Note The DFF Component by default does not show the preset or reset terminals („ar‟ in Figure 5). To enable these terminals,
configure the Component as Figure 6 shows.
Figure 6. DFF Component Configuration
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Code 1. Interrupt-Based Response to Input Pin Transitions
uint8 count; /* # of transitions of input pin 'SW' */
CY_ISR(SwInt_ISR)
{
SwReset_Write(1); /* clear interrupt source */
count++;
} /* end of SwInt_ISR() */
void main()
{
uint8 temp; /* local copy of count variable */
/* Initialization code */
. . .
for(;;) /* do forever */
{
/* Grab a copy of the shared count variable, and display the copy.
* This ensures the interrupt handler will not change the count
* variable while it is being displayed.
*/
CYGlobalIntDisable; /* macro */
temp = count;
CYGlobalIntEnable; /* macro */
LCD_Position(0, 14); /* row, column */
LCD_PrintHexUint8(temp);
}
} /* end of main() */
The display increments with each button press and button
release. However if you run the attached project
„A_DebounceNone‟, you see that the display sometimes
increments several times on a single button press or
release. The reason becomes apparent if you connect an
oscilloscope to both the input switch pin and the interrupt
test pin; see Figure 7.
The system is running at high speed. This allows each
interrupt to be processed in a very short time relative to
the transitions rate. Thus, instead of a single edge, every
edge is detected and processed. (If you look closely at
Figure 7, you can see that even the very narrow first pulse
generates two interrupts.)
To solve this problem, you must use a switch debouncing
technique. The remainder of this application note shows
various ways to do so.
Figure 7. Scope Shot Showing Switch Bounce and
Interrupt Response
Input
switch pin
Interrupt
test pin
Note that PSoC pins are capable of directly generating an edge-triggered interrupt through the port interrupt control unit
(PICU). However, the PICU cannot be used in this application because the interrupts occur on pin transition edges and not at
regular sample intervals. Thus, a PICU-based design is subject to the same switch bounce problems noted in Figure 5.
The PICU can also cause pin transitions to wake up the PSoC from a low-power mode, such as Sleep or Hibernate. In this
case, you can create a design in which a debounce operation is suspended when entering a low-power mode and restarted
after wakeup. For more information on PSoC power modes, see application note AN77900 for PSoC 3 or PSoC 5LP, or
AN86233 for PSoC 4.
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Switch Debouncing by Sampling
There are many ways to do switch debouncing, but all of
them involve sampling the input pin at a periodic rate.
Figure 8. Scope Shot Showing Switch Transition Time
Set the sample period to be greater than the anticipated
transition time of the signal, that is, the time it takes for the
signal to stabilize at the new state when the switch is
opened or closed. During the transition time, the state of
the signal is essentially unknown – at any time it could be
either 0 or 1. You should not sample more than once
during that period or you may detect an extra transition.
The maximum sample rate is the inverse of the maximum
transition time; remember that you may need to check
both the low-to-high and high-to-low transition times.
Transition time
The example in Figure 8 shows that the maximum
transition time from pressed to released is ~300 μs. In this
case, the sampling rate should not exceed 1 / (300 μs), or
3.3k samples per second (sps).
In practice, set the sample rate to be much lower than the expected transition time, but fast enough that the system is
responsive when the switch is opened or closed. A rate of 10 to 200 sps is usually appropriate.
Switch Debouncing Using Software
The simplest way to sample a switch is to poll the input pin, that is, program the CPU to read the pin‟s input value at regul ar
time intervals. In Code 2 on page 7, the pin is sampled at an interval that is controlled by the CyDelay() function provided by
PSoC Creator.
The easiest way to detect a transition on the input is to use two variables, for current and previous values of the pin, and
compare them for transition events.
The example in Code 2 monitors just one pin, in bit 0 of each element of the „switches‟ array. In this case, we compare the
array elements in their entirety, with the assumption that bits 1 to 7 are always zero. If you need to monitor multiple pins then
you can either:


use a separate pair of variables for each pin, or
use a single pair of variables, with a bit defined for each pin
There are tradeoffs in code size, execution speed, and RAM memory usage, for each method.
With PSoC, you can monitor a pin in software and hardware at the same time. The attached project „B_DebounceSwPoll‟ adds
to project „A_DebounceNone‟ to show both raw (unfiltered) and filtered counts.
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Code 2. Periodic Sampling of an Input Pin
void main()
{
/* Initialization code */
. . .
/* Init switch variables */
uint8 switches[2] = {0, 0}; /* [0] = current, [1] = previous */
switches[0] = switches[1] = SW_Read(); /* 0 = pressed, 1 = not pressed */
/* Init display */
LCD_Start();
LCD_Position(0, 0); /* row, column */
LCD_PrintString("Raw Count
= ");
LCD_Position(1, 0); /* row, column */
LCD_PrintString("Filt. Count = ");
for(;;) /* do forever */
{
/* Place your application code here. */
/* Grab a copy of the shared count variable, and display the copy.
* This is so that the interrupt handler won't change the count
* variable while it's being displayed.
*/
CyGlobalIntDisable; /* macro */
temp = count;
CyGlobalIntEnable; /* macro */
LCD_Position(0, 14); /* row, column */
LCD_PrintHexUint8(temp);
/* Periodically sample the input pin, and display the filtered count */
CyDelay(50); /* msec */
/* Update the current and previous switch read values */
switches[1] = switches[0];
switches[0] = SW_Read();
/* Increment counter if a switch transitions either way */
if (switches[0] != switches[1])
{
filtered_count++;
}
/* Display the current value in filtered count variable */
LCD_Position(1, 14); /* row, column */
LCD_PrintHexUint8(filtered_count);
}
} /* end of main() */
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
With code that must do many tasks, it may be difficult to
poll a pin at regular intervals. In that case, an alternative is
to sample by using a periodic interrupt. The easiest way to
do this, for PSoC 3 and PSoC 5LP, is to connect a Clock
Component directly to an Interrupt Component, as
Figure 9 shows.
Figure 9. Components for Periodic Interrupts
PSoC 4 does not support routing a clock directly to an
interrupt. The easiest workaround is to double the clock
frequency and route it through a TFF Component, as
Figure 10 shows. The TFF Component output is half the
frequency of the input clock.
Figure 10. PSoC 4 Components for Periodic Interrupts
In both cases, the Interrupt Component „SampInt‟ must be set as a rising edge triggered interrupt, so that the interrupt is
triggered only once per clock period – see Figure 11.
Figure 11. SampInt Configuration
In this design, as Code 3 on page 9 shows, the sample interrupt handler does the sampling and edge detection. This makes
the main() function much simpler. The attached project „C_DebounceSwInt‟ contains similar code, to show both raw
(unfiltered) and filtered counts
For more information on interrupts in PSoC, see AN54460, PSoC Interrupts.
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Code 3. Interrupt-Based Sampling of an Input Pin
uint8 filtered_count; /* # of filtered transitions of input pin 'SW' */
CY_ISR(SampInt_ISR)
{
static uint8 init = 0;
static uint8 switches[2]; /* [0] = current, [1] = previous */
uint8 temp;
/* interrupting from clock, no interrupt source to clear */
temp = SW_Read(); /* read the pin value */
/* Switch variable initialization should be done only once, the first
* time this function is called.
*/
if (!init)
{
init = 1;
switches[0] = switches[1] = temp;
}
else
{ /* Increment the count if the switch transitions either way. */
switches[1] = switches[0];
switches[0] = temp;
if (switches[0] != switches[1])
{
filtered_count++;
}
}
} /* end of SampInt_ISR */
void main()
{
uint8 temp; /* local copy of shared count variable */
/* Initialization code */
. . .
for(;;) /* do forever */
{
. . .
/* Grab a copy of the shared filtered count variable, and display the
* copy. This is so that the interrupt handler won't change the count
* variable while it's being displayed.
*/
CYGlobalIntDisable /* macro */
temp = filtered_count;
CYGlobalIntEnable /* macro */
LCD_Position(1, 14); /* row, column */
LCD_PrintHexUint8(temp);
}
} /* end of main() */
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Switch Debouncing Using Hardware
PSoC makes it easy to do switch debouncing in hardware
instead of software, which can reduce CPU usage. The
simplest way to do this is to poll with a clock and a status
register, as Figure 12 shows.
Figure 12. Schematic of a Design with Register-based
Switch Debouncing
The code for this design is the same as in Code 2 except
that you read from PinReg_Status instead of SW_Read(),
and the CyDelay() function is removed. See attached
project „D_DebounceHwReg‟.
Debouncer Component
You can reduce CPU usage even more by moving both the input pin polling and the comparison functions into hardware. The
PSoC Creator Component library includes a Debouncer Component that is designed for this purpose.
Figure 13 shows a design using the Debouncer Component. As shown previously in Figure 11 on page 8, make sure that the
FiltInt Component is configured for RISING_EDGE mode.
Figure 13. Design Using a Debouncer Component
Note The output of the Debouncer is reset to „0‟ at device reset, and the input switch is read as „1‟ when it is open, which is the
typical case. This results in a single false switch release event at initialization. An inverter on the input pin solves this problem.
This design also includes a Status Reg Component, so that the CPU can read the type of edge that caused the interrupt. The
Status Reg Component is configured for “sticky 1” mode. In this mode, when a bit is set to „1‟, it stays that way until the
register is read by the CPU or DMA, at which point it is reset to „0‟.
Most of the debounce functions are now performed in hardware instead of software, so the interrupt handler is simplified; see
Code 4. The code in main() remains unchanged except for some initialization.
Code 4. Interrupt-based Response to Hardware Debouncer Component
uint8 filtered_count; /* # of filtered transitions of input pin 'SW' */
CY_ISR(FiltInt_ISR)
{
/* No need to clear any interrupt source; interrupt component should be
* configured for RISING_EDGE mode.
*/
/* Read the debouncer status reg just to clear it, no need to check its
* contents in this application.
*/
FiltReg_Read();
filtered_count++;
} /* end of FiltInt_ISR() */
It is not necessary to connect a Debouncer Component output terminal to an Interrupt Component. Depending on the
application, you can connect any of the terminals to other digital logic or to a DMA channel.
You can easily add support for multiple pins by changing the Component‟s signal width parameter.
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Glitch Filtering
Glitch filtering is similar to switch debouncing but supports a slightly different application. In switch debouncing, you filter out all
edges except the single one that you want. In glitch filtering, you remove unwanted glitch pulses from a signal.
Note that glitches are not necessarily associated with switches; they can occur on lines carrying signals from sources such as
RF receivers. Electrical or in some cases even mechanical interference can trigger an unwanted glitch pulse from a receiver.
The switch debouncing methods shown previously “mostly” work for glitch filtering but never 100 percent, because you might
sample just when a glitch is occurring. Instead, the glitch filter algorithm outputs a „1‟ only when the current and previous N
samples are „1‟, and a „0‟ only when the current and previous N samples are „0‟. Otherwise, the output remains unchanged
from its current value.
If N = 1 then the time between two successive samples (SP in Figure 14) must be greater than the maximum pulse width that
can be filtered (MaxPW). Because it takes at least two samples for the output to change, the response time, or filter delay, is
between 1 and 2 sample periods.
Figure 14. Glitch Filter Performance for N = 1
PW
Input
SP
Samples
Output
SP > PW, SP < response time < 2 SP
The response time can also be expressed in terms of the MaxPW. In the case for N = 1, because the sample period can be as
low as the maximum filtered pulse width, the response time can range from 1 to 2 times the MaxPW.
You can use larger values of N to get more deterministic and possibly shorter response times. For example, if N = 2, the
response time is between 2 and 3 sample periods. However the sample period can be shorter – the MaxPW must be less than
2 sample periods – and thus the response time can be expressed as 1 to 1.5 times the MaxPW. See Figure 15.
Figure 15. Glitch Filter Performance for N = 2
PW
Input
Samples
Output
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SP
SP > PW / 2, 2 SP < response time < 3 SP
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
If N = 3 then the response time can range from 1 to 1.333 times the MaxPW, and so on. The general response time equations
are:
Equation 1. Glitch Filter Response Time
N  SP  response time 
SP 
N  1 SP
MaxPW
N
MaxPW  response time 
 1  1  MaxPW
 N


where SP = sample period, and MaxPW = maximum filtered pulse width.
Most glitch filters are designed with N = 1, 2, or 3. Note that in a hardware-based design, larger values of N require more
PSoC digital resources to implement.
Figure 16 shows a design using a PSoC Creator Glitch
Filter Component. The clock frequency is the sample
period. As shown previously in Figure 11 on page 8, make
sure that the FiltInt Component is configured for
RISING_EDGE mode.
Figure 16. Design Using a Glitch Filter Component
Note The output of the Glitch Filter is reset to „0‟ at device
reset, and the input switch is read as „1‟ when it is open,
which is the typical case. This results in a single false
release event at initialization. An inverter on the input pin
solves this problem.
It is not necessary to connect the Glitch Filter Component‟s output terminal to an Interrupt Component. Depending on the
application, you can connect it to other digital logic or to a DMA channel.
You can easily add support for multiple pins by changing the Component‟s signal width parameter.
Although a switch debouncer is not a 100 percent effective glitch filter, a glitch filter can be an effective switch debouncer.
However, glitch filters may be overkill for a basic switch debouncing application. The Glitch Filter Component uses
approximately 20% more PSoC UDB PLD resources than the Debouncer Component.
Summary
We can now come full circle back
to the original design shown in
Figure 5 on page 4, except that we
add a Glitch Filter component
between the pin and the DFFs, as
Figure 17 shows. The design is no
longer sensitive to switch bounce.
Figure 17. Design from Figure 5 with a Glitch Filter Added
Similar to Figure 13 and Figure 16,
we add an inverter to eliminate the
initial false reset event.
The Glitch Filter clock also clocks
the FiltReset Control Reg. This
ensures a reliable reset when
writing to the Control Reg.
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Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Switch debouncing and glitch filtering are an essential part of processing digital input signals. This application note has shown
several ways to implement them, using different combinations of hardware and software.
There are many opportunities to optimize these designs for specific applications. For example:

All of the designs capture both positive and negative edges. If you are interested in only one edge, you can simplify the
design in hardware or software.

To support multiple digital inputs, you can scale the design either by using multiple bits in a register or variable or by
setting the signal width parameter of the Debouncer or GlitchFilter Component.
Design Projects
Related Application Notes
The projects attached to this application note are
organized as shown in Table 1.





AN54181, Getting Started with PSoC 3

AN82156, PSoC Designing PSoC Creator
Components with UDB Datapaths

AN77900, PSoC 3 and PSoC 5LP Power Reduction
Techniques


AN86233, PSoC 4 Power Reduction Techniques
Table 1. Debounce Projects
Design Project
Name
Description
A_DebounceNone
Demonstrates extra counts
recorded in the absence of switch
debouncing – how NOT to do the
design.
B_DebounceSwPoll
Demonstrates switch debouncing
by software sampling of an input
pin at periodic intervals.
C_DebounceSwInt
Demonstrates switch debouncing
using an interrupt driven by a lowfrequency clock.
D_DebounceHwReg
Demonstrates switch debouncing
by connecting the input pin to a
status register with a low-frequency
clock.
E_DebounceHw
Demonstration project for the
Debouncer Component.
F_GlitchFilter
Demonstration project for the Glitch
Filter Component.
www.cypress.com
AN79953, Getting Started with PSoC 4
AN77759, Getting Started with PSoC 5LP
AN81623, PSoC Digital Design Best Practices
AN82250, PSoC Implementing Programmable
Designs with Verilog
AN54460, PSoC Interrupts
About the Author
Name:
Mark Ainsworth
Title:
Applications Engineer Principal
Background:
Mark Ainsworth has a BS in Computer
Engineering from Syracuse University
and an MSEE from University of
Washington, as well as many years
experience designing and building
embedded systems.
Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Document History
®
Document Title: Switch Debouncer and Glitch Filter with PSoC 3, PSoC 4, and PSoC 5LP - AN60024
Document Number: 001-60024
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
2895472
FSU
03/18/2010
New application note
*A
2901010
FSU
03/31/2010
Attached associated project to the application note
*B
2991584
SRIH
07/22/2010
Fixed branding discrepancies
*C
3010675
XKJ
08/18/2010
Updated projects to Beta 5
*D
3068548
KLMZ
10/22/2010
Updated D_DebounceSwInt project and the corresponding content in the
application note to use an edge triggered interrupt instead of a control register.
*E
3137066
MKEA
01/13/2011
Updated project files to work with PSoC Creator 1.0 FCS
*F
3370231
MKEA
09/14/2011
Expanded content and improved project based on customer feedback
*G
3393004
MKEA
10/12/2011
Project file renamed properly and attached
*H
3432788
MKEA
11/08/2011
Updated template and project file
*I
3441058
MKEA
12/16/2011
Simplified Debouncer component
*J
3538104
MKEA
02/29/2012
Added references for more information on PSoC Creator library projects and
updated template
*K
3718792
MKEA
08/23/2012
Added Table of Contents.
*L
3819424
MKEA
11/22/2012
Updated for PSoC 5LP and PSoC Creator 2.1 SP1
*M
4088648
MKEA
08/08/2013
Updated for PSoC 4 and PSoC Creator 2.2 SP1. Projects modified to use PSoC
Creator standard Debouncer and Glitch Filter Components.
*N
4258095
MKEA
01/22/2014
Corrected Code listings to match attached projects. Corrected some reference
links. Miscellaneous minor edits.
*O
4364538
MKEA
04/28/2014
Updated for PSoC Creator 3.0. Added a section on UDBs. Minor edits and
formatting changes.
www.cypress.com
Document No. 001-60024 Rev. *O
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Switch Debouncer and Glitch Filter with PSoC® 3, PSoC 4, and PSoC 5LP
Worldwide Sales and Design Support
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cypress.com/go/plc
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PSoC is a registered trademark and PSoC Creator is a trademark of Cypress Semiconductor Corp. All other trademarks or registered trademarks
referenced herein are the property of their respective owners.
Cypress Semiconductor
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San Jose, CA 95134-1709
Phone
Fax
Website
: 408-943-2600
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: www.cypress.com
© Cypress Semiconductor Corporation, 2010 - 2014. The information contained herein is subject to change without notice. Cypress Semiconductor
Corporation assumes no responsibility for the use of any circuitry other than circuitry embodied in a Cypress product. Nor does it convey or imply any
license under patent or other rights. Cypress products are not warranted nor intended to be used for medical, life support, life saving, critical control or
safety applications, unless pursuant to an express written agreement with Cypress. Furthermore, Cypress does not authorize its products for use as
critical components in life-support systems where a malfunction or failure may reasonably be expected to result in significant injury to the user. The
inclusion of Cypress products in life-support systems application implies that the manufacturer assumes all risk of such use and in doing so indemnifies
Cypress against all charges.
This Source Code (software and/or firmware) is owned by Cypress Semiconductor Corporation (Cypress) and is protected by and subject to worldwide
patent protection (United States and foreign), United States copyright laws and international treaty provisions. Cypress hereby grants to licensee a
personal, non-exclusive, non-transferable license to copy, use, modify, create derivative works of, and compile the Cypress Source Code and derivative
works for the sole purpose of creating custom software and or firmware in support of licensee product to be used only in conjunction with a Cypress
integrated circuit as specified in the applicable agreement. Any reproduction, modification, translation, compilation, or representation of this Source
Code except as specified above is prohibited without the express written permission of Cypress.
Disclaimer: CYPRESS MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARD TO THIS MATERIAL, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Cypress reserves the
right to make changes without further notice to the materials described herein. Cypress does not assume any liability arising out of the application or
use of any product or circuit described herein. Cypress does not authorize its products for use as critical components in life-support systems where a
malfunction or failure may reasonably be expected to result in significant injury to the user. The inclusion of Cypress‟ product in a life-support systems
application implies that the manufacturer assumes all risk of such use and in doing so indemnifies Cypress against all charges.
Use may be limited by and subject to the applicable Cypress software license agreement.
www.cypress.com
Document No. 001-60024 Rev. *O
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