Urahara
Member
Hi
Am trying to understand a C pgm (believe it is Hi-Tech's C) written for 16F877A to work with a 4x4 keypad. Within the scan subroutine, there is a statement that says asm("nop") with a comment saying it is for delay purpose. Is there a reason for using this statement instead of a "for" loop? Also, is this an interrupt-based scanning? This is supposedly the complete demo pgm I've gotten.
Finally, does anyone has a C18 code for a 4x4 keypad scanning? Hv searched but seems to be getting only assembly-based examples. I am trying to do one for a 18F4550.
Thks!
Am trying to understand a C pgm (believe it is Hi-Tech's C) written for 16F877A to work with a 4x4 keypad. Within the scan subroutine, there is a statement that says asm("nop") with a comment saying it is for delay purpose. Is there a reason for using this statement instead of a "for" loop? Also, is this an interrupt-based scanning? This is supposedly the complete demo pgm I've gotten.
Code:
#include<pic.h> //include MCU head file
__CONFIG(0x1832);
//THE configure of MCU,watchdog OFF,electrify delay OPEN,power down check OFF,
//LOW power programme OFF,encrypt,4M crystal HS surge.
int result;
void delay(); //delay function declare
void init(); //I/O PORT initialize function declare
void scan(); //key scan function declare
void display(int x); //display function declare
//---------------------------------------------------
//main program
void main()
{
while(1) //circle work
{
init(); //call initialize subprogram
scan(); //call key scan subprogram
display(result); //call result display subprogram
}
}
//---------------------------------------------------
//initialize function
void init()
{
ADCON1=0X07; // set A PORT general I/O PORT
TRISA=0X0f; //A PORT low 4 bits INPUT,high 4 bits OUTPUT
TRISC=0XF0; //C PORT high 4 bits INPUT,low 4 bits OUTPUT
TRISD=0X00; //set D PORT OUTPUT
PORTA=0XFF;
PORTD=0XFF; //clear all display
}
//---------------------------------------------------
//key scan program
void scan()
{
PORTC=0XF7; //C3 OUTPUT low,the other 3 bits OUTPUT high
asm("nop"); //delay
result=PORTC; //read C PORT
result=result&0xf0; //clear low 4 bits
if(result!=0xf0) //judge if high 4 bits all 1(all 1 is no key press)
{
result=result|0x07; //no,add low 4 bits 0x07 as key scan result
}
else //yes,change low 4 bits OUTPUT, judge if a key press again
{
PORTC=0XFb; //C2 OUTPUT low,the other 3 bits OUTPUT high
asm("nop"); //delay
result=PORTC; //read C PORT
result=result&0xf0; //clear low 4 bits
if(result!=0xf0) //judge if high 4 bits all 1(all 1 is no key press)
{
result=result|0x0b; //no,add low 4 bits 0x0b as key scan result
}
else //yes,change low 4 bits OUTPUT, judge if a key press again
{
PORTC=0XFd; //C1 OUTPUT low,the other 3 bits OUTPUT high
asm("nop"); //delay
result=PORTC; //read C PORT
result=result&0xf0; //clear low 4 bits
if(result!=0xf0) //judge if high 4 bits all 1(all 1 is no key press)
{
result=result|0x0d; //no,add low 4 bits 0x0d as key scan result
}
else //yes,change low 4 bits OUTPUT, judge if a key press again
{
PORTC=0XFe; //C0 OUTPUT low,the other 3 bits OUTPUT high
asm("nop"); //delay
result=PORTC; //read C PORT
result=result&0xf0;//clear low 4 bits
if(result!=0xf0) //judge if high 4 bits all 1(all 1 is no key press)
{
result=result|0x0e;//no,add low 4 bits 0x0e as key scan result
}
else //yes,all key scan end,no key press,set no key press flag
{
result=0xff; //key scan result 0xff as no key press flag
}
}
}
}
}
//----------------------------------------------------------
//display program
void display(int x)
{
switch(result)
{
case 0xe7:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xc0;PORTA=0X1F;delay();break; //K10
case 0xeb:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xf9;PORTA=0X1F;delay();break; //K11
case 0xed:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xa4;PORTA=0X1F;delay();break; //K12
case 0xee:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xb0;PORTA=0X1F;delay();break; //K13
case 0xd7:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0x99;PORTA=0X1F;delay();break; //K14
case 0xdb:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0x92;PORTA=0X1F;delay();break; //K15
case 0xdd:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0X82;PORTA=0X1F;delay();break; //K16
case 0xde:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0XF8;PORTA=0X1F;delay();break; //K17
case 0xb7:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0X80;PORTA=0X1F;delay();break; //K18
case 0xbb:
PORTD=0xf9;PORTA=0X2F;delay();PORTD=0X90;PORTA=0X1F;delay();break; //K19
case 0xbd:
PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xc0;PORTA=0X1F;delay();break; //K20
case 0xbe:
PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xf9;PORTA=0X1F;delay();break; //K21
case 0x77:
PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xa4;PORTA=0X1F;delay();break; //K22
case 0x7b:
PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xb0;PORTA=0X1F;delay();break; //K23
case 0x7d:
PORTD=0xa4;PORTA=0X2F;delay();PORTD=0x99;PORTA=0X1F;delay();break; //K24
case 0x7e:
PORTD=0xa4;PORTA=0X2F;delay();PORTD=0x92;PORTA=0X1F;delay();break; //K25
case 0xff:
PORTD=0x8e;PORTA=0X2F;delay(); PORTD=0x8e; PORTA=0X1F; delay(); //no key press
}
}
//------------------------------------------------------------------
//delay program
void delay() //delay program
{
int i; //define integer variable
for(i=0x100;i--;); //delay
}Finally, does anyone has a C18 code for a 4x4 keypad scanning? Hv searched but seems to be getting only assembly-based examples. I am trying to do one for a 18F4550.
Thks!