AN2034 PSoC 1 - Reading Matrix and Common Bus Keypads.pdf

AN2034
PSoC® 1 – Reading Matrix and Common Bus Keypads
Author: Dave Van Ess, Rajiv Badiger
Associated Project: Yes
Associated Part Family: CY8C27xxx, CY8C29xxx,
CY8C21x23, CY8C21x34,CY8C21x45, CY8C22x45,
CY8C24x23, CY8C24x94, CY8C28xxx
®
Software Version: PSoC Designer™ 5.4
Related Application Notes: None
®
AN2034 shows how to use PSoC 1 to read mechanical keypads. It covers matrix and common bus keypads, in both polled
and interrupt modes.
Contents
Introduction
Introduction .......................................................................1
Matrix Keypad ...................................................................2
Algorithm ......................................................................2
C Function ....................................................................2
Decoding a Key Press ..................................................3
Debounce Mechanism ..................................................3
Making the Scanning Process Polled or
Interrupt Driven.............................................................4
Example Project ...........................................................4
Common Bus Keypad .......................................................5
PSoC 1 Implementation................................................5
SAR ADC Input Voltages..............................................6
Determining Resistor Values ........................................7
Interrupt Driven Keypad Reading .................................7
Debouncing ..................................................................7
Example Project ...........................................................7
Summary ...........................................................................8
Appendix A: ‘C’ Code for Matrix Keypad Scanning
Using Interrupt Method ......................................................9
Appendix B: ‘C’ Code for Common Bus Keypad
Using Polling Method ...................................................... 14
Document History ............................................................ 17
Depending on how individual switches are connected,
mechanical keypads are commonly available in two
forms – matrix and common bus.
A typical matrix keypad – the telephone keypad - is shown
in Figure 1. In this keypad, each switch connects a unique
pair of row and column wires. The number of I/Os (pins)
required equals ROWS + COLUMNS. The number of
switches supported is ROWS x COLUMNS.
Figure 1. Matrix Keypad
In a common bus keypad, one terminal of each switch is
connected to a common bus wire as shown in Figure 2.
www.cypress.com
Document No. 001-40409 Rev. *E
1
PSoC® 1 - Reading Matrix and Common Bus Keypads
Figure 2. Common Bus Keypad
significant CPU time. If only a single key press needs to
be detected, you can use the following algorithm instead:
The number of I/Os required for a common bus keypad
appears to equal the number of switches plus 1, however,
a method exists that uses only one pin to read the
common bus keypads.
This application note shows how to use PSoC 1 to read
both the matrix and common bus keypads. The associated
projects are created using the PSoC Designer software
tool. If you are new to the PSoC 1 device or the
PSoC Designer development tool, it is recommended that
you review the online tutorials.
Matrix Keypad
This section focuses on a typical 4x4 matrix keypad, but
you can use the same technique with a matrix keypad of
any dimensions. A matrix keypad can be connected to the
PSoC 1 without using any external components as shown
in Figure 3.
Figure 3. Matrix Keypad Interface to PSoC 1

Drive all columns high simultaneously and read all
rows

Combine the above data to determine which switch is
closed
To understand how the algorithm works, consider the
following example, where switch [1, 2] (row 1, column 2) is
pressed. The algorithm reads the keypad in six steps.
1.
Output b00001111 to the port. This drives all the rows
high, leaving the columns passively pulled down.
2.
Read the port. The driven pins 0 through 3 remain
high, and because the switch [1, 2] is closed pin 6 is
now high. The value read is b01001111.
3.
Output b11110000 to the port. This drives all the
columns high, leaving the rows passively pulled down.
4.
Read the port. The driven pins 4 through 7 remain
high, and because the switch [1, 2] is closed pin 1 is
now high. The value read is b11110010.
5.
Do a logical AND of the results of steps 2 and 4 to get
the answer b01000010.
6.
The upper 4 bits can be decoded as column 2 and the
lower 4 bits as row 1.
The above algorithm can be implemented as a function
keypad_scan(). It reads a 4x4 keypad connected to port 0
and returns the ANDed result, as shown in Code 1:
R0
1
CPU
Drive all rows high simultaneously and read all
columns
C Function
4 x 4 Matrix Keypad
0

[0,0]
[0,1]
[0,2]
[0,3]
[1,0]
[1,1]
[1,2]
[1,3]
[2,0]
[2,1]
[2,2]
[2,3]
2
3
R1
Code 1. Keypad Scan Function
4
5
6
R2
/*
This is the port mapping for the keypad
ports.
7
PSoC 1
Port Data
register
R3
[3,0]
[3,1]
C0
[3,2]
C1
[3,3]
C2
C3
PSoC 1 pins are highly flexible and can be configured in
many different modes, such as strong drive, resistive
pull-up, resistive pull-down, open drain drive high/low, and
high impedance. To avoid a floating input when no key is
pressed, use the resistive pull-down mode for all row and
column pins.
Algorithm
The standard algorithm for reading a matrix keypad is to
drive each row high, one at a time, and sample the column
lines. This technique enables detection of multiple key
presses. However, scanning the entire keypad takes
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p0.0 ---1----2----3----A
|
|
|
|
p0.1 ---4----5----6----B
|
|
|
|
p0.2 ---7----8----9----C
|
|
|
|
p0.3 ---*----0----#----D
|
|
|
|
p0.4 p0.5 p0.6 p0.7
*/
unsigned char keypad_scan(void)
{
unsigned char rows;
unsigned char cols;
/* Drive rows, read columns */
PRT0DR = 0x0F;
cols = PRT0DR;
Document No. 001-40409 Rev. *E
2
PSoC® 1 - Reading Matrix and Common Bus Keypads
presses. One way to handle this problem is to implement a
delay from when the first edge is detected (A or C) to
when the ports are read (B or D). This delay ensures that
the signal at the port pins is stable during the CPU read
operation. A delay of 10 ms is usually sufficient for most
types of switches.
/* Drive columns, read rows*/
PRT0DR = 0xF0;
rows = PRT0DR;
/* combine results */
return (rows & cols);


No bits are set if no key is pressed
A delay can be implemented using a firmware or a
hardware timer. The disadvantage of a firmware delay is
that it requires the CPU. In an application where the CPU
must do many tasks, it is better to generate the delay
using a hardware timer. PSoC 1’s configurable digital
blocks make it possible to create such a timer; it is
available in the form of a PSoC Designer user module
named Timer.
A single bit in the upper nibble and a single bit in the
lower nibble are set for a single key press
To add a debounce delay using a hardware timer, do the
following:

Any other condition is a multiple key closure and is
defined as not valid
1.
}
Decoding a Key Press
The output of the keypad_scan() function is a single byte
that shows the row or column status of the keypad. It is
decoded as follows:
You will usually need to translate the row or column bits
into a more useful form, for example an ASCII character
corresponding to the key press. The most speed efficient
way to do this is to use a lookup table (LUT) array. For a
size efficient implementation, use switch case statements.
Place a Timer user module in the design, as shown in
Figure 5:
Figure 5. Timer User Module
In this project, the LUT method is used: the byte output of
the keypad_scan() function is used as an index to a
256-byte array. In the 4x4 keypad case, 16 elements in
the array contain codes corresponding to valid key
presses, and the remaining elements contain codes for
"no key press" or "undefined". See Appendix A: ‘C’ Code
for Matrix Keypad Scanning Using Interrupt Method for
details.
2.
Debounce Mechanism
When any key is pressed or released, due to mechanical
structure, the contacts may make or break connection
multiple times. Due to this, an oscillating waveform can be
obtained at the row or column line as shown in Figure 4:
You can also use an 8-bit timer, which consumes one
less digital block, with a lower input clock frequency to
generate the same delay. The input clock to a timer
can be derived using internal clock dividers VC1, VC2,
and VC3.
Figure 4. Key Bounce
Key is pressed
Key is released
3.
time
Stable state
Debounce
delay
A
Configure the timer clock input and period to generate
the required delay. As an example, a 16-bit timer is
configured with a 32 kHz internal low-speed oscillator
(ILO) input clock, with a period of 320 counts, to
generate a delay of 10 ms.
The Timer user module can generate an interrupt, and
you can call the keypad scanning function from the
Timer interrupt service routine (ISR). This will cause
the CPU to read the ports after a debounce delay.
Debounce
delay
B
C
D
If the CPU reads the ports at a high rate, the bounce
oscillations may be wrongly detected as multiple key
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Document No. 001-40409 Rev. *E
3
PSoC® 1 - Reading Matrix and Common Bus Keypads
Making the Scanning Process Polled or
Interrupt Driven
Figure 6. Interrupt and Debounce Action
Key is pressed
Key is released
The scanning algorithm in the keypad_scan() function can
be executed once the key press is detected. There are two
ways to call the function and detect key activity - polling
and interrupt.
With the polling method, the CPU periodically scans the
keypad to check if any key is pressed. The CPU can either
read the keypad in a while loop or can be interrupted at
regular intervals using a timer. The scan period must be
greater than the debounce delay and less than the
minimum key press time. The problem with this method is
that most of the time the keys are not pressed, and doing
a scan during those times is a waste of CPU cycles. A
better way is to do a scan only when a key press event is
detected.
With the interrupt method, the CPU can be interrupted on
a key press. The ISR then starts the timer for a debounce
delay and a keypad scan is done at the timer interrupt.
To configure PSoC for an interrupt-based method, do the
following:

Configure the four lower (row) pins (see Figure 3) as
inputs, with resistive pull-down


Drive the four upper (column) pins high

Enable the GPIO interrupt
Write a GPIO interrupt handler that enables the timer,
for a debounce delay
The row pins stay low when no key is pressed. On a key
press, the rising edge signal is produced on one of the row
lines which trigger an interrupt. The GPIO ISR enables the
timer for a debounce delay. After the delay, the Timer ISR
does the scan. See Figure 6 for more details.
time
Stable state
Debounce
delay
A
Debounce
delay
B
C
D
A
Key is pressed. Rising edge signal interrupts CPU. CPU
starts the timer for debounce delay
B
Debounce delay elapsed. Timer triggers interrupt to the
CPU to read the ports to identify the key pressed.
C
Key is released. Rising edge signal interrupts CPU once
again. CPU starts the timer for debounce delay
D
Debounce delay elapsed. Timer triggers interrupt to the
CPU to read port once again. As key is released, no key
press will be detected.
* Note that switch may not bounce during switch release and C and
D events may not occur.
The interrupt method also helps to reduce the power
consumption by allowing the device to be put in sleep
mode. When any key is pressed, the resulting interrupt
can wake the device.
Note that the PSoC 1 interrupt system combines the
interrupt signals from all of the pins in the device to
generate a single interrupt. Thus, any key press will trigger
a common interrupt. However, any other external event
will also trigger the same interrupt. To handle this you may
need to have the ISR read other ports to determine the
cause of the interrupt.
Example Project
The PSoC Designer project “MatrixKeypad”, based on
PSoC 1 CY8C27443, is provided. The project uses the
interrupt method and is configured for the external
connections shown in Figure 7. In the project, the closed
key is displayed on a Hitachi-compatible 2x16 character
LCD. The number of times any key is pressed is also
displayed to evaluate the debounce logic. If the debounce
logic is working correctly, you will notice that the count
increments only once on each key press. See Appendix A:
‘C’ Code for Matrix Keypad Scanning Using Interrupt
Method for the application firmware.
www.cypress.com
Document No. 001-40409 Rev. *E
4
PSoC® 1 - Reading Matrix and Common Bus Keypads
Figure 7. External Connections for Testing "MatrixKeypad"
Project
Hitachi compatible
2x16 character
LCD module
D0
D1
D2
D3
EN
Character LCD
RS
R/W
P2[0]
P0[0]
1
2
3
A
P0[1]
4
5
6
B
P0[2]
7
8
9
C
P0[3]
*
0
#
D
Common Bus Keypad
This section shows how to read an 8-key common bus
keypad using only one PSoC pin. The logic behind the
single pin solution is to generate a distinct analog voltage
on a key press and to decode it using the ADC. The block
diagram of the solution is given in Figure 8.
P2[1]
P2[2]
A switch-resistor network forms a voltage divider
connected between the power supply (VDD) and the
ground (VSS). The PSoC 1 ADC is configured to read the
input voltage from VDD to VSS. The resistor values are
chosen so that when a particular switch is pressed, the
input voltage to the ADC is within a certain range. A
simple algorithm can be created that compares the ADC
result with the predetermined codes to identify the key
pressed.
P2[3]
P2[4]
P2[5]
PSoC 1
P0[4]
P2[6]
P0[5]
P0[6]
+5V
Vdd
GND
Contrast
control
voltage
P0[7]
When multiple keys are pressed, the one which is closer
to the pin takes priority; the resistor network beyond the
closed key is bypassed. In Figure 8, S0 has the highest
priority and S7 has the lowest priority.
Figure 8. Block Diagram - Common Bus Keypad Interface to PSoC
VDD
R0
ADC
R1
S0
R2
S1
S2
R3
R4
S3
S4
R5
S5
R6
S6
R7
S7
PSoC 1
Keypad
VSS
PSoC 1 Implementation

PSoC Designer provides different types of ADCs that are
implemented using generic analog blocks in PSoC 1.
Consumes one PSoC 1 switched capacitor (SC)
analog block

Produces a 1 byte 2’s complement output, ranging
from -32 to +31
The resolution of the ADC is an important parameter for
this application as it determines the number of switches
N
that can be interfaced. Ideally, with an N-bit ADC 2
switches can be read. But due to the tolerances of the
resistors, it is significantly lower.
To read an 8-switch keypad, a 6-bit SAR ADC is sufficient.
The SAR ADC is available in the form of a user module in
PSoC Designer. This user module has the following
features:
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Table 1. SAR ADC Input to Output Mapping
Input Voltage (VIN)
Digital Output
AGND (analog ground)
00h
AGND < VIN < VH
00h to 1Fh
VL < VIN < AGND
E0 to FFh
Document No. 001-40409 Rev. *E
Comments
RefMux setting in
Global resources
tab of PSoC
Designer decides
VH and VL and
AGND.
5
PSoC® 1 - Reading Matrix and Common Bus Keypads
The input impedance of the SAR ADC is in the kΩ range; it
depends on the frequency of the clock to the SC block. To
avoid errors due to low input impedance, place a
programmable gain amplifier (PGA) module between the
SAR ADC and the external network. The PGA uses a
PSoC 1 continuous time (CT) analog block which has high
input impedance.
Figure 10. Global Resource Settings
Using PSoC Designer, configure the PSoC 1 as follows:

Place the PGA and SAR ADC user modules on the
design

Route the PGA input to a pin connected to the
external switch-resistor network, as shown in Figure 9.
Figure 9. User Modules Placement and Routing
SAR ADC Input Voltages
When mapped uniformly for a VDD of 5.0 V, each switch
produces a nominal increase of 5.0 V / 8 = 0.625 V, or a
12.5 percent change in the ADC input voltage. Table 2
provides the input voltage range for the ADC for each
switch. The midpoint of each range is the theoretical ADC
input voltage neglecting all error sources such as resistor
tolerances, ADC error, noise, and so on.
Table 2. Mapping Switch Press to the Voltage Generated





Switch
Voltage Range at
Input
Byte
Range
Resistor
Value
S0
0 V – 0.3125 V
[E0 – E4]
-
S1
0.3125 V – 0.9375 V
[E4 – EC]
R1 = 1.5 kΩ
Route the PGA output to the SAR ADC input
S2
0.9375 V – 1.5625 V
[EC – F4]
R2 = 1.8 kΩ
Set the PGA gain to 1 in the PGA module properties
S3
1.5625 V – 2.1875 V
[F4 – FC]
R3 = 2.7 kΩ
Set the analog column clock to VC2, with the
frequency between 128 kHz and 1.33 MHz in the
global resource settings. This clock controls the
switching frequency of the SC block.
S4
2.1875 V – 2.8125 V
[FC – 04]
R4 = 4.3 kΩ
S5
2.8125 V – 3.4375 V
[04 – 0C]
R5 = 6.8 kΩ
S6
3.4375 V – 4.0625 V
[0C – 14]
R6 = 13 kΩ
In the global resources tab, set the VC2 frequency to
1 MHz by setting the VC1 divider to 12 and the VC2
divider to 2, as shown in Figure 10. Note that the
system clock (SysClk) of the PSoC 1 device is
24 MHz.
S7
4.0625 V – 4.6875 V
[14 – 1A]
R7 = 33 kΩ
No
Switch
5.0 V
1F
-
Also in the global resources tab, set the RefMux
option to (VDD/2) +/- (VDD/2). This sets the SAR ADC
measurement range as 0 to VDD, and the AGND
voltage to VDD/2.
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If none of the switches are closed, the input to the ADC is
equal to VDD. When S0 is closed, current flows from VDD to
VSS through R0 and S0. A value of 10 kΩ was chosen for
R0 to limit the maximum supply current to 0.5 mA. The
remaining resistors are calculated based on VDD = 5 V,
R0 = 10 kΩ, and a nominal step size of 0.625 V for each
switch. The following section explains how to select the
resistors.
Document No. 001-40409 Rev. *E
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PSoC® 1 - Reading Matrix and Common Bus Keypads
Determining Resistor Values
Basic resistor voltage divider analysis can be used to
determine the resistor values. Consider the case when
switch S1 is pressed (see Figure 8)
Solving for R1 and inserting nominal values for V DD and
R0 gives
The closest ±5% standard value resistor is 1.5 kΩ. With
R1 = 1.5 kΩ and R0 = 10 kΩ, the typical ADC input
voltage with S1 closed is 0.652 V. This error is acceptable
since it falls within the allowed voltage range for SW1, that
is, 0.3125 V to 0.9375 V. Moreover, with the worst case
resistor tolerances (R0 = 10 kΩ – 5% and R1 = 1.5 kΩ +
5%, or R0 = 10 kΩ + 5% and R1 = 1.5 kΩ – 5%), the input
voltage deviates by just 0.059 V from the ideal value.
The same type of analysis can be used to determine the
remaining resistor values, which are provided in Table 2.
The interrupt pin is pulled low using a resistor (R). When
any key is pressed, the rising edge signal is developed
across R causing an interrupt to the device. The value of
the resistor R must be high enough so that the voltage
developed across it, on any key press, is greater than the
VIH specification for a GPIO (minimum 2.1 V).
After an interrupt is generated, the interrupt pin is
grounded by writing a ‘0’ to the port data register. This
causes the resistor R to be bypassed while reading the
voltage using the ADC. Note that the lower end of the
switches is not exactly 0 V - it is lifted above the ground by
a few millivolts depending on the sink current value. Using
the higher value of resistor R0 limits the sink current and
thus the voltage lift. For this application, use R0 of 10 kΩ
or higher.
Debouncing
It is possible for a switch press or release to occur during
an ADC conversion, which would result in an erroneous
output. To avoid these errors, you can implement a
debounce mechanism similar to that for the matrix keypad:

Configure the timer user module to generate a delay
of at least 10 ms

If an interrupt method is used, start the timer when the
GPIO interrupt is detected. For the polling method,
start the timer when the ADC reads a value different
from the "no keys pressed" value.

At the timer interrupt, read the ADC. If the ADC
reading is same as the previous reading, a key can be
assumed to be pressed and stable.
Interrupt Driven Keypad Reading
As seen in the section Making the Scanning Process
Polled or Interrupt Driven, it is better to read the ADC on
an interrupt when any key is pressed rather than reading
the ADC continuously. This saves CPU bandwidth as well
as device power consumption if sleep mode is used. To
make the process interrupt driven, one more pin must be
used for generating an interrupt signal. See Figure 11 for
external connections.
Figure 11. Interrupt Driven Scanning Process
Vdd
Example Project
The project "CommonBusKeypad", based on the
CY8C27443 PSoC 1 device, uses the polling method. The
complete code is also provided in Appendix B: ‘C’ Code
for Common Bus Keypad Using Polling Method. The
project can be tested with the external connections shown
in Figure 12. In the project, key presses are displayed on a
Hitachi-compatible 2x16 character LCD.
R0
ADC
R1
S0
Interrupt signal
PSoC1
S1
R2
S2
Rn
Sn
Keypad
R
Vss
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Document No. 001-40409 Rev. *E
7
PSoC® 1 - Reading Matrix and Common Bus Keypads
Figure 12. External Connections for Testing “CommonBusKeypad” Project
Hitachi compatible
2x16 character
LCD module
D0
D1
D2
D3
EN
Character LCD
RS
R/W
Vdd=+5V
P2[0]
P2[1]
R
P2[2]
P2[3]
P0[2]
P2[4]
R1
R2
R3
S0
P2[6]
S1
S2
S3
PSoC1
+5V
R4
R5
R6
R7
P2[5]
S4
S5
S6
S7
Keypad
Vdd
GND
Contrast
control
voltage
Use the resistor values R and R1 to R7 as shown in Table 2.
Summary
About the Author
This application note shows easy methods to read matrix
type and a common bus type keypads using PSoC 1. It
also explains the polling and the interrupt mechanisms for
keypad scanning as well as debounce logic.
www.cypress.com
Name:
Rajiv Badiger
Title:
Applications Engineer
Background:
BE Electronics and Telecommunication
Contact:
[email protected]
Document No. 001-40409 Rev. *E
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PSoC® 1 - Reading Matrix and Common Bus Keypads
Appendix A: ‘C’ Code for Matrix Keypad Scanning Using Interrupt Method
#include <m8c.h> // part specific constants and macros
#include "PSoCAPI.h" // PSoC API definitions for all User Modules
/*****************Variables***************************/
/* LUT for storing keys. The size of the LUT should be equal to 2 ^ (NUMBER OF ROWS +
COLUMNS). Row and column information from the scanning function is used as index to this LUT
for finding the key. Value 0x20 indicates invalid key. */
static const keypad_LUT[256] =
{/*
0
1
2
3
4
5
6
7
8
9
A
B
C
D
E
F */
/*0*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*1*/0x20, '1', '4', 0x20, '7', 0x20, 0x20, 0x20,
'*', 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*2*/0x20, '2', '5', 0x20, '8', 0x20, 0x20, 0x20,
'0', 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*3*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*4*/0x20, '3', '6', 0x20, '9', 0x20, 0x20, 0x20,
'#', 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*5*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*6*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*7*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*8*/0x20, 'A', 'B', 0x20, 'C', 0x20, 0x20, 0x20,
'D', 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*9*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*A*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*B*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*C*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*D*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*E*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
/*F*/0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20
};
/* These two variables are used to store the row number and the column number */
BYTE rows,cols;
/* This variable holds the count for number of key press */
BYTE InterruptCounter = 0;
/* This variable keeps the scanning process disabled till previously decoded key is read */
unsigned char processing = 0;
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PSoC® 1 - Reading Matrix and Common Bus Keypads
/* These variable stores the key number */
unsigned char key = 0x20;
/*****************************************************/
/****************Functions****************************/
/* Handles keypad function- Checks the key pressed and debounces key */
void KeyPadHandler(void);
/* Keypad scanning routine */
unsigned char keypad_scan(void);
/* Initializes user modules used in the design */
void InitModules(void);
/* Interrupt handler for GPIO interrupt */
void GPIOInterrupt(void);
/****************************************************/
void main(void)
{
/* Initialize variables and user modules */
InitModules();
/* Enable Global Interrupt */
M8C_EnableGInt;
while(1)
{
/* Check the Keypad status and update LCD on valid key press */
if(key != 0x20)
{
/* Valid key- display the result on LCD */
/* Set LCD cursor position */
LCD_1_Position(0, 7);
/* Display pressed keypad button */
LCD_1_WriteData(key);
/* Set LCD cursor position */
LCD_1_Position(1, 12);
/* Display nuymber of times key is pressed so far */
LCD_1_PrHexByte(InterruptCounter);
/* Reset key to default value */
key = 0x20;
/* Enable keypad scanning process */
processing = 0;
}
/* Do other tasks */
}
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PSoC® 1 - Reading Matrix and Common Bus Keypads
}
/* This function initializes all the user modules used in the design */
void InitModules(void)
{
/* Initialize LCD */
LCD_1_Start();
LCD_1_Position(0,0);
LCD_1_PrCString("Switch:");
LCD_1_Position(1,0);
LCD_1_PrCString("Interrupts:");
/* Initilize timer- 10ms delay */
Timer16_1_WritePeriod(320);
Timer16_1_EnableInt();
/* Enable GPIO interrupt */
INT_MSK0 |= 0x20;
/* Write 1's at column lines */
PRT0DR |= 0xF0;
}
/*
This is the port mapping for the keypad ports.
p0.0
p0.1
p0.2
p0.3
p0.4 p0.5 p0.6 p0.7
|
|
|
|
---1----2----3----A
|
|
|
|
---4----5----6----B
|
|
|
|
---7----8----9----C
|
|
|
|
---*----0----#----D
*/
/* This function scan the keypad and identifies the key pressed */
unsigned char keypad_scan(void)
{
BYTE key_result;
/* Drive rows */
PRT0DR = 0x0F;
/* Read columns */
cols = PRT0DR;
/* Drive columns */
PRT0DR = 0xF0;
/* Read rows */
rows = PRT0DR;
/* Combine results */
key_result = rows & cols;
/* Get the key number from LUT */
return(keypad_LUT[key_result]);
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PSoC® 1 - Reading Matrix and Common Bus Keypads
}
/* This is the handler for GPIO interrupt. Debounce timer is started on GPIO interrupt */
#pragma interrupt_handler GPIOInterrupt
void GPIOInterrupt(void)
{
/* Check if previous key is read. If yes, start the timer for debounce delay */
if(processing == 0)
{
/* Avoid enabling timer next time when previous key is not read */
processing = 1;
/* Disable GPIO interrupt */
INT_MSK0 &=~ 0x20;
/* Start Timer */
Timer16_1_Start();
}
}
/* This is the handler for the timer interrupt. This ISR calls the scanning algorithm */
void TimerInterrupt(void)
{
/* Stop the timer */
Timer16_1_Stop();
/* Get the key */
key = keypad_scan();
/* Check for valid key press */
if(key != 0x20)
{
/*********************************************************/
/* Add code here to take immediate action within the ISR */
/********************************************************/
/* Increment interrupt counter */
InterruptCounter ++;
}
else
{
/* Enable starting the timer on GPIO interrupt */
processing = 0;
}
/* Clear GPIO posted interrupt */
INT_CLR0 &=~ 0x20;
/* Enable GPIO interrupt */
INT_MSK0 |= 0x20;
}
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PSoC® 1 - Reading Matrix and Common Bus Keypads
Add LJMP instruction in PSoC_GPIO_ISR function in PSoCGPIOINT.asm file as shown in the following code.
PSoC_GPIO_ISR:
;@[email protected] (Do not change this line.)
;--------------------------------------------------; Insert your custom code below this banner
;--------------------------------------------------ljmp _GPIOInterrupt
;--------------------------------------------------; Insert your custom code above this banner
;--------------------------------------------------;@[email protected] (Do not change this line.)
reti
Add LCALL instruction in Timer16_1_ISR function in Timer16_1NT.asm file as shown below.
_Timer16_1_ISR:
;@[email protected] (Do not change this line.)
;--------------------------------------------------; Insert your custom assembly code below this banner
;--------------------------------------------------;
NOTE: interrupt service routines must preserve
;
the values of the A and X CPU registers.
;--------------------------------------------------; Insert your custom assembly code above this banner
;--------------------------------------------------;--------------------------------------------------; Insert a lcall to a C function below this banner
; and un-comment the lines between these banners
;--------------------------------------------------PRESERVE_CPU_CONTEXT
lcall _TimerInterrupt
RESTORE_CPU_CONTEXT
;--------------------------------------------------; Insert a lcall to a C function above this banner
; and un-comment the lines between these banners
;--------------------------------------------------;@[email protected] (Do not change this line.)
reti
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PSoC® 1 - Reading Matrix and Common Bus Keypads
Appendix B: ‘C’ Code for Common Bus Keypad Using Polling Method
#include <m8c.h> // part specific constants and macros
#include "PSoCAPI.h" // PSoC API definitions for all User Modules
/* Timer State */
#define ON 0x1
#define OFF 0x0
/* Invalid Key identifier */
#define INVALID_KEY 0x20
/* Functions */
char Get_ADC_Data(void);
void GetKeyNumber(void);
/* Variables */
BYTE Key = INVALID_KEY, TimerState = OFF;
char ADC_Data,New_ADC_Data;
void main(void)
{
/* Enable Timer Interrupt */
Timer16_1_EnableInt();
/* Enable Global Interrupt */
M8C_EnableGInt ;
/* Start PGA operation in high power mode */
PGA_1_Start(PGA_1_HIGHPOWER);
/* Start ADC operation */
SAR6_1_Start(SAR6_1_HIGHPOWER);
/* Start LCD and Initialize Display */
LCD_1_Start();
LCD_1_Position(0,0);
LCD_1_PrCString("Switch:");
while(1)
{
/* If timer is OFF (debounce is not in process), check the "key" */
if(TimerState == OFF)
{
/* If "Key" contains valid value, then display on LCD */
if(Key != INVALID_KEY)
{
LCD_1_Position(0,7);
LCD_1_PrHexByte(Key);
/* Invalidate Key */
Key = INVALID_KEY;
}
else /* No Key Pressed */
{
LCD_1_Position(0,7);
LCD_1_PrCString("--");
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PSoC® 1 - Reading Matrix and Common Bus Keypads
}
/* Get ADC data */
ADC_Data = SAR6_1_cGetSample();
/* Check if any key is pressed */
if(ADC_Data < 0x1C || ADC_Data > 0xE0)
{
/* Start Timer */
Timer16_1_Start();
TimerState = ON;
}
}
/* Do other tasks */
}
}
/* Interrupt Handler for Timer Interrupt */
void TimerInt(void)
{
BYTE Delta = 0;
/* Take a second sample, compare with the first to test
data validity in the presence of possible switch bounce */
New_ADC_Data = SAR6_1_cGetSample();
/* Compare the ADC values and get the difference */
if(ADC_Data > New_ADC_Data)
{
Delta = ADC_Data - New_ADC_Data;
}
else
Delta = New_ADC_Data - ADC_Data;
/* If difference in readings is less than 2, then decode the key */
if(Delta < 2)
{
/* If closely matched, decode the key */
GetKeyNumber();
}
/* Stop the timer */
Timer16_1_Stop();
TimerState = OFF;
}
/* This function decodes the key. See Table 2 of application note for ADC result to Key
mapping information */
void GetKeyNumber(void)
{
if((New_ADC_Data > 0xE0) && (New_ADC_Data <= 0xE4))
Key = 0;
else if((New_ADC_Data > 0xE4) && (New_ADC_Data <= 0xEC))
Key = 1;
else if((New_ADC_Data > 0xEC) && (New_ADC_Data <= 0xF4))
Key = 2;
else if((New_ADC_Data > 0xF4) && (New_ADC_Data <= 0xFC))
Key = 3;
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PSoC® 1 - Reading Matrix and Common Bus Keypads
else if((New_ADC_Data > 0xFC)
Key = 4;
else if((New_ADC_Data >= 0x0)
Key = 4;
else if((New_ADC_Data > 0x04)
Key = 5;
else if((New_ADC_Data > 0x0C)
Key = 6;
else if((New_ADC_Data > 0x14)
Key = 7;
else
Key = INVALID_KEY;
&& (New_ADC_Data <= 0xFF))
&& (New_ADC_Data <= 0x04))
&& (New_ADC_Data <= 0x0C))
&& (New_ADC_Data <= 0x14))
&& (New_ADC_Data <= 0x1A))
}
Add LCALL instruction in Timer16_1_ISR function in Timer16_1NT.asm file as shown in the following code.
_Timer16_1_ISR:
;@[email protected] (Do not change this line.)
;--------------------------------------------------; Insert your custom assembly code below this banner
;--------------------------------------------------;
NOTE: interrupt service routines must preserve
;
the values of the A and X CPU registers.
;--------------------------------------------------; Insert your custom assembly code above this banner
;--------------------------------------------------;--------------------------------------------------; Insert a lcall to a C function below this banner
; and un-comment the lines between these banners
;--------------------------------------------------PRESERVE_CPU_CONTEXT
lcall _TimerInt
RESTORE_CPU_CONTEXT
;--------------------------------------------------; Insert a lcall to a C function above this banner
; and un-comment the lines between these banners
;--------------------------------------------------;@[email protected] (Do not change this line.)
reti
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PSoC® 1 - Reading Matrix and Common Bus Keypads
Document History
®
Document Title: PSoC 1 - Reading Matrix and Common Bus Keypads – AN2034
Document Number: 001-40409
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
1532004
OGNE
10/02/2007
New publication of existing application note.
*A
2640952
JVY
01/20/2009
Updated content.
Added part numbers CY8C20x34, CY8C21x23, CY8C21x34, CY8C23x33,
CY8C24x23A, CY8C24x94, CY8C27x43, and CY8C29x66.
*B
3312765
OWEN
07/19/2011
Added section about LED display, converted code to C from assembly, updated
associated project similarly.
*C
3416292
RJVB
10/24/2011
Added common bus keypad interface details, introduced debounce logic and
interrupt mechanism.
Updated template
*D
3433993
RJVB
11/09/2011
Modified title and updated project code in Appendix A and B
*E
4463001
ARVI
08/01/2014
Updated example projects to PSoC Designer v5.4
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Document No. 001-40409 Rev. *E
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PSoC® 1 - Reading Matrix and Common Bus Keypads
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