AN205508
F²MC-8FX Family, MB95200 Series Keyboard development using AD
This application note describes how to use the AD Conversion to design the keyboard and also describes the
realization theories of AD conversion by examples.
Contents
1
2
Introduction ...............................................................1
Introduction to AD Function ......................................1
2.1
Function of AD Conversion ..............................1
2.2
Jittering Elimination in Keyboard......................1
3
Hardware Design ......................................................2
3.1
Hardware Circuit ..............................................2
3.2
Relationship between Key Status and
Input Voltage ..................................................2
4
Resource Usage .......................................................3
4.1
8/10-bit A/D Converter Control Register 1
(ADC1) .............................................................3
1
4.2
5
6
7
8
8/10-bit A/D Converter Control Register 2
(ADC2) ............................................................ 4
4.3
8/10-bit A/D Converter Data Registers
Upper/Lower (ADDH, ADDL) ........................... 5
4.4
AD Converter Process ..................................... 5
Software Design ....................................................... 6
Sample Code............................................................ 7
Additional Information ............................................... 9
Document History ................................................... 10
Introduction
There are three methods to develop a keyboard by MB95200 series MCU: external interrupt, AD conversion and
matrix.
This document describes how to use the AD Conversion to design the keyboard.
This document also describes the realization theories of AD conversion by examples.
2
Introduction to AD Function
This chapter introduces the functions of using AD Conversion to realize the keyboard.
2.1
Function of AD Conversion
The function of AD Convertor is to convert an analog voltage (input voltage) value on an analog input pin to a 10-bit
digital value. The MCU of MB95200 series has at least 2 analog input pins. When AD convertor is enabled, the
analog input signal on the selected channel will be sampled and compared inside the AD convertor and finally
converted to a digital value stored into the A/D converter data register (ADDH, ADDL).
2.2
Jittering Elimination in Keyboard
Jittering elimination has been one of important problems in keyboard design. In hardware circuit design, add a
capacitor to the analog input pin to weaken the jittering, while in software design, re-confirm the data to avoid jittering
occurred on a real keyboard.
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3
Hardware Design
This chapter introduces the hardware design to develop keyboard using AD Conversion.
3.1
Hardware Circuit
The resistors in the following hardware circuit are designed to divide voltage. And the analog input pin will get a
different voltage from the circuit. The following circuit is for your reference:
Figure 1. Hardware Design for Keyboard Using AD
3.2
Relationship between Key Status and Input Voltage
Table 1. Relationship between Key Status and Input Voltage
Pressed key
AN00 Voltage
ADDL value
Virtual value
SW1
0V
0x00
0x00>=ADDL<=0x05
SW2
2.5 V
0x7F
0x79>=ADDL<=0x85
SW3
3.3 V
0xAA
0xA1>=ADDL<=0xB2
SW4
3.75 V
0xBF
0xB5>=ADDL<=0xC8
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F²MC-8FX Family, MB95200 Series Keyboard development using AD
4
Resource Usage
This chapter introduces the resource usage of AD Conversion.
Please refer to Chapter 17 of MB95200 Series Hardware Manual for detailed register setting.
4.1
8/10-bit A/D Converter Control Register 1 (ADC1)
The 8/10-bit A/D converter control register 1 (ADC1) is used to enable and disable individual functions of the 8/10-bit
A/D converter, select an analog input pin and check the status of the converter.
Figure 2. ADC1 Register
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4.2
8/10-bit A/D Converter Control Register 2 (ADC2)
The 8/10-bit A/D converter control register 2 (ADC2) is used to control different functions of the 8/10-bit A/D
converter, select the input clock, and enable and disable interrupts.
Figure 3. ADC2 Register
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4.3
8/10-bit A/D Converter Data Registers Upper/Lower (ADDH, ADDL)
The 8/10-bit A/D converter data registers upper/lower (ADDH, ADDL) store the results of 10- bit A/D conversion
during 10-bit A/D conversion. The upper two bits of 10-bit data are stored in the ADDH register and the lower eight
bits the ADDL register.
Figure 4. AD Data Registers
The upper two bits of 10-bit A/D data correspond to bit1 and bit0 in the ADDH register and the lower eight bits bit15 to
bit8 in the ADDL register.
If the AD8 bit in ADC2 register is set to "1", 8-bit precision is selected. Reading the ADDL register can obtain 8-bit
data.
4.4
AD Converter Process
After the conversion time according to the register settings elapses, the results of conversion are finalized and stored
in the ADDH and ADDL registers. After A/D conversion is completed and before the next A/D conversion is started,
it's required to read A/D data registers (conversion results) and clear ADI flag bit (bit 3) in the ADC1 register.
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F²MC-8FX Family, MB95200 Series Keyboard development using AD
5
Software Design
This chapter introduces the software design to develop keyboard using AD conversion.
Once the AD convertor is enabled, it will capture the status information of keyboard. If the value (Distem0) belongs to
the key-value, restored it, if not, the AD Convertor continues to sample. After this, stop the AD Convertor and make
the system wait for about 20ms, then restart the AD Convertor and get a sample value (Distem1) again. Finally, judge
this value to see if it is equal to Distem0. If it is different from Distem0, it is regarded that jittering happens; otherwise,
judge which key has been pressed.
Below is the flow chart of this software design.
Figure 5. Software Design Flow Chart for Keyboard Development
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Sample Code
This chapter illustrates keyboard development using AD Conversion.
The following example shows how to use the AD Conversion input pin AN00 to design a 4- key keyboard.
As discussed in chapter 5, if using AD Conversion to design a keyboard system, initialize the AD Conversion first,
then AD conversion starts sampling, and gets an sample value, read this value and judge that if it belongs to the keyvalue. if does not, system continues to sample; if does, stop the AD Conversion and let the system waits for about 20
ms, and then restart AD Conversion, get an another sample value. If the two sample values are the same, it shows
that one of the keys has been pressed; if not, it shows only a jittering happens.
#include "../MB95200_IO/mb95200.h". . .
void clock_Select(void)
// Main clock initialize
{
SYCC = 0x00;
WATR = 0x00;
STBC = 0x01;
SYCC2= 0xF4;
}
void syinit(void)
{
DDR0_P00 = 0;
//P00 input enable
ADC1 = 0x01;
//AN00 as input
ADC2 = 0x80;
//8-bit resolution,1×MCLK
ADC1_AD = 1;
//start A/D converter
DDR0 = 0xF0;
//P4~P7 as output pin
PUL0 = 0x00;
AIDRL = 0xFE;
}
void timer_init(void)
{
TMCR0 = 0x10;
// 16-bit
T00CR0 = 0x81;
// interval timer with continuous mode
T00CR1 = 0xA0;
// disable output, start timer
T01DR = 0x27;
// 10000us
T00DR = 0x10;
while(STBC_MRDY);
}
__interrupt void Timer_Interrupt (void)
{
T00CR1_IF = 0;
T00CR1_IE = 0;
timer_counter++;
if(timer_counter==1) // Read and store ADDL in value 1
{
AD_Sample();
}
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F²MC-8FX Family, MB95200 Series Keyboard development using AD
if(timer_counter==2)
// Read and store ADDL in value 2 and
compare value and value 2
{
key_judge();
}
if(timer_counter>=3)
{
timer_counter=0;
}
/Timer_counter restart
}
void AD_Sample(void)
{
if(ADC1_ADI==1)
{
while(!ADC1_ADI);
Distem0 = ADD_ADDL; // Read AD Sample value 1
}
ADC1_AD=1;
// Start AD again
}
void key_judge(void)
{
if(ADC1_ADI==1)
// Read and store ADDL in value 2
{
while(!ADC1_ADI);
Distem1 = ADD_ADDL;
}
if(Distem1==Distem0) // Judge if value 1 and value 2 equality
{
if(Distem1 == Range_value0) // Key process
{
DDR0_P04 = 1;
PDR0_P04 = 0;
}
if((Distem1 >= Range_value1)&&(Distem1 <= Range_value2))
{
DDR0_P05 = 1;
PDR0_P05 = 0;
}
if((Distem1 >= Range_value3)&&(Distem1 <= Range_value4))
{
DDR0_P06 = 1;
PDR0_P06 = 0;
}
if((Distem1 >= Range_value5)&&(Distem1 <= Range_value6))
{
DDR0_P07 = 1;
PDR0_P07 = 0;
}
}
}
void main(void)
{
InitIrqLevels();
//initialise Interrupt level and IRQ vector table
__EI();
// global interrupt enable
clock_Select();
while(1)
{
syinit();
timer_init();
}
}
Note: This sample project is based on our starter-kit MB2146-410A. The target MCU is MB95F304K. AN0 is used as
an analog input pin, and LED1 to LED4 an indicator. If keyboard hardware circuit as shown in chapter 3.1 is not
provided, stop a jumper and connect VR3 to MCU so that VR3 can be used as an analog input. Then observe how
LED changes in adjusting VR3.
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F²MC-8FX Family, MB95200 Series Keyboard development using AD
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Additional Information
For more Information on MB95200 Products, visit the following website:
http://www.cypress.com/8fx-mb95200
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Document History
Document Title: AN205508 - F²MC-8FX Family, MB95200 Series Keyboard development using AD
Document Number: 002-05508
Revision
ECN
Orig. of
Change
Submission
Date
Description of Change
**
-
HUAL
02/24/2009
Initial release
*A
5264394
HUAL
05/13/2016
Migrated Spansion Application Note MCU-AN-500037-E-10 to Cypress
format
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F²MC-8FX Family, MB95200 Series Keyboard development using AD
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