Question

18) Referring to the PIC16F877A Data Sheet and Parallax 27899 4 Matrix-Membrane-Keypad, please complete the following: x4 Write Pseudocode in the form of a Flow Chart that would be necessary for use entering data into Registers on the PIC16F877A Microcontroller. You are going to need to research this. Please refer to Keypad Interfacing PIC16F877A found on Bb under Supplemental Materials. Do not use Assembly language. Please write clearly, make your Flow Chart Clean and Clear. Provide comments on all relevant lines of your Pseudocode. Your Pseudocode will need to correspond with the Electrical connections seen in the Schematic below. X4 KEYPAD

Answer 1

in c

#include <hidef.h> /* common defines and macros */
#include <mc9s12dp256.h> /* derivative information */
#include <stdio.h>
#include "lcd.h"
#pragma LINK_INFO DERIVATIVE "mc9s12dp256b"

//scan row and return any key pressed
//returns null if no key pressed
//will only return one character pressed at a time
char keyScanner(int row);

void main( void )
{
char data[17] = {" "}; //string to be sent to lcd
char string[17]; //string to be sent to lcd
int arrayIndex = 0; //current index in string
int scanrow; //which row hcs12 is scanning
unsigned long delay; //used for delay in key debouncing
  
LCD_init(); /* Enable the LCD display */
  
//Enable keypad
DDRA = 0xf0; //upper 4 bits control which row to scan, lower 4 bits are keypad

sprintf(string,"Type on the ");
writeLine(string, 0);
sprintf(string,"keypad. ");
writeLine(string, 1);
while(1) //loop forever
{
for(scanrow=0; scanrow < 4; scanrow++) //start scanning rows
{
char key = keyScanner(scanrow); //get current key
  
if (key) //if key is pressed
{
for(delay=0; delay < 120000; delay++); //delay for debouncing
  
if (key == keyScanner(scanrow)) //check to see if key is still pressed
{
data[arrayIndex] = key; //set current index in string to current key pressed
  
if (arrayIndex < 15) //make sure we are not exceeding limits of lcd
{
arrayIndex++; //move to next index
}
else
{
arrayIndex = 0; //overflow, start index over
}
writeLine(data, 0); //write new data to lcd line 0
sprintf(string,"%c=%d in ASCII ", key, key);
writeLine(string, 1);
}
}
}
}
}

//scan row and return any key pressed
//returns null character if no key pressed
//will only return one character pressed at a time
char keyScanner(int row)
{
unsigned char rowCode[4] = {0x10, 0x20, 0x40, 0x80}; //lookup table for rows to scan
unsigned char keyCode[4][4] = {{49, 50, 51, 65},
{52, 53, 54, 66},
{55, 56, 57, 67},
{42, 48, 35, 68}}; //lookup table for ascii value of key
  
PORTA = rowCode[row]; //set row to scan
  
if (PORTA & 0x01) //first key in row
{
return keyCode[row][0];
}
else if (PORTA & 0x02) //second key in row
{
return keyCode[row][1];
}
else if (PORTA & 0x04) //third key in row
{
return keyCode[row][2];
}
else if (PORTA & 0x08) //fourth key in row
{
return keyCode[row][3];
}
  
return '\0'; //no key pressed, return null character
}