Hi All,
I'm trying to set up a menu on my serial 4x20 LCD (from NetMedia)
and am wondering why my key press delay_ms(500) code isn't effective;
in other words, after a button is pressed, I'm expecting the delay to
take effect, but it doesn't; the program can loop hundreds of times
instead of only once during that button press. I added some counters
in-line to see this. I realize I am not otherwise debouncing the
buttons; I'm simply looking at the port and acting on the state of
the port; all PortD pins have external 10k pull-up resistors, so I'm
assuming any activity on PortD is initiated by button presses.

Here is what the menu looks like:

        MAIN MENU
        ->Run Automatically
          Run Manually
          Setup

The bottom three lines of the LCD are menu items, and I'm reading
three buttons on PortD, called Next, Previous and Select in a
while loop. For example, when the Next button is pressed, the display
is supposed to be updated - the select arrow moved to the next menu
item or wrapped up to the first menu item. Monitoring the value of
NextCtr in a watch window, I see that if I press the Next button 5
times in about 2 seconds, and then stop the ICD, the NextCtr reads
well over 1000; and the menu may or may not have been updated
correctly.

Below is the code fragment. I'm working in PICC, (PCM compiler 3.092)
for the PIC16F877 using the MicroChip ICD.


I am curious to know why the program can appear to bypass the delay
routine and welcome any suggestions to improve my menu code or design.
I think I am overlooking something basic, but I'm not sure what.

Thanks in advance!

Patrick Murphy
James Valley Colony


long NextCtr, PrevCtr;
NextCtr = 0; // Count the number of times this portion of code is active.
PrevCtr = 0; // Also count in the Previous Button code.

pspmode = 0;  // Set up PortD
PORTD = 0xFF; // Make PORTD inputs
TRISD = 0xFF;
ArrowLine = 1; // Current LCD line counter

// Loop while waiting for user input: Next, Previous, or Select buttons.
while(MenuState == MainMenu0)           //Monitor lower 5 PortD inputs
{
        PDButtons = PORTD;
        PDButtons = ~PDButtons; // Invert so button pressed is now high
        switch (PDButtons)
        {
                case 0x01:  // Select Button Pressed: PortD0. Selected new menu.
                        porta1 = 1;  // Porta1 LED for debugging. No delay necessary.
                        if (ArrowLine == 1)
                                MenuState = Automatic1;
                        else if (ArrowLine == 2)
                                MenuState = Manual2;
                        else if (ArrowLine == 3)
                                MenuState = Setup3;
                        break;
                case 0x02: // Next Button Pressed: PortD1. Move arrow down or wrap.
                        porta2 = 1;  // Porta2 LED for debugging.
                        NextCtr++;
                        if (ArrowLine < 3)
                        {
                                ArrowLine++;
                        }
                        else
                        {
                                ArrowLine = 1;
                        }
                        printf(ser_char, "  ");
                        ser_lcd_cursor_pos(0, ArrowLine); // col, line
                        printf(ser_char, "->");
                        ser_lcd_cursor_pos(0, ArrowLine); // col, line
                        delay_ms(500);
                        break;
                case 0x04: // Previous Button Pressed: PortD2. Move arrow up or wrap.
                        porta3 = 1;
                        PrevCtr++;
                        if (ArrowLine > 1)
                        {
                                ArrowLine--;
                        }
                        else
                        {
                                ArrowLine = 3;
                        }
                        printf(ser_char, "  ");
                        ser_lcd_cursor_pos(0, ArrowLine); // col, line
                        printf(ser_char, "->");
                        ser_lcd_cursor_pos(0, ArrowLine); // col, line
                        delay_ms(500);
                        break;
                case 0x08: // Up Button Pressed: PortD3. Not used in this menu.
                        porta5 = 1;
                        delay_ms(100);
                        break;
                case 0x10: // Down Button Pressed: PortD4. Not used in this menu.
                        portb0 = 1;
                        delay_ms(100);
        }// switch
        porta1 = 0; Turn off debugging LED's
        porta2 = 0;
        porta3 = 0;
        porta5 = 0;
        portb0 = 0;
} // while(MenuState == MainMenu0)


void delay_10us(byte t)
// provides delay of t * 10 usecs (4.0 MHz clock)
{
#asm
      BCF STATUS, RP0
DELAY_10US_1:
      CLRWDT
      NOP
      NOP
      NOP
      NOP
      NOP
      NOP
      DECFSZ t, F
      GOTO DELAY_10US_1
#endasm
}

void delay_ms(long t)   // delays t millisecs (4.0 MHz clock)
{
   do
   {
     delay_10us(100);
   } while(--t);
}

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