button pullup/down resistor?

[davewanna]

I have been working for days on an RF project, and I suspect I'm going crazy.

I have put a button on my 16F877a just so I can tell it to do something.
The problem is, that when I press the button it activates, but when I let go of it, it stays activated.

I have gone as low as a 560ohm pullup/down resistor. Tried pulling to ground, and to +5V.

I am currently using pin D.0

TRISD = %10000000
but  VAR PORTD.0
....

Start:

lcdout $fe,$80,"Rec  ",dec counter
lcdout $fe,$c0,bin result,"   "
lcdout $fe,$d4,bin stats,"   "

if but = 1 then
  lcdout $fe,$8A,"B"
  gosub chkstatus
else
  lcdout $fe,$8A," "
endif

if nIRQ = 0 then
  lcdout $fe,$94,"Receiving!"
  gosub receive
else
  lcdout $fe,$94,"Waiting..."
endif

pause 50
counter = counter + 1

goto start

With a 560ohm to +5v, and the button to ground. After it has been pressed, and depressed - I am still measuring 185mV on pin D.0. Even after I remove the jump wire to the button entirely, I am still reading 185mV on the pic with only the resistor connected to +5v.


HOWEVER... If I take the jump wire from pin D.0 and connect it straight to +5v, and then to ground. The display and functions work as expected.

How could I have done this? I have tried 2 different (new) 877a's, and several port pins.

Running on 10MHz, 5V regulated, smoothing caps, on a breadboard.

[skimask]

Running on 10MHz, 5V regulated, smoothing caps, on a breadboard.

That would be my first suspect right there.

Other than that, forget about everything else that you may/may not have going on in your program.
Write a small routine to display the button input status on the LCD and NOTHING ELSE!
And use pull ups.

but var portd.0 : input but
Start:
lcdout $fe , $80 , "Button="
if but = 1 then
lcdout $fe , $87 , "On "
else
lcdout $fe , $87 , "Off"
endif
goto start

That should hook you up with all the info you need.

[davewanna]

Simplified, and still not working.

DEFINE OSC 4

' Define LCD registers and bits
DEFINE  LCD_DREG        PORTC            'LCD addressing
DEFINE  LCD_DBIT        4                'L1 = $80         
DEFINE  LCD_RSREG       PORTD            'L2 = $C0 
DEFINE  LCD_RSBIT       2                'L3 = $94
DEFINE  LCD_EREG        PORTD            'L4 = $D4
DEFINE  LCD_EBIT        3

TRISD = %10000000
but	var portd.0

lcdout $fe,1
Start:

if but = 0 then
  lcdout $fe,$8A,"On "
else
  lcdout $fe,$8A,"Off"
endif

goto start

Shows "off" on the screen until I press the button - then says "on" and stays that way, even after button released

I went back to a 4Mhz clock, and have measured voltages and resistances to ground and +5v on d.0 (pin 19)

[skimask]

TRISD = %10000000

Take a good hard look at that line.

[davewanna]

I'm a dickhead...

I'm trying to make RF work, and I don't even know how to set a TRIS.....

So after reading the datasheet again, and doing some tests... It seems I've been setting the TRIS as LSB first, when it should be MSB first... Correct?

Must just be pure luck that my previous projects have worked.

Thanks Skimask.. You've been a big help on most all of my queries so far.

[skimask]

I'm a dickhead...

I wouldn't go that far!

So after reading the datasheet again, and doing some tests... It seems I've been setting the TRIS as LSB first, when it should be MSB first... Correct?

It was either that or you had your ins and outs mixed up.
1 = input = because it looks like the letter I for input
0 = output = because it looks like the letter O for output
MSB is on the left, just like in a regular written number (unless it's in Arabic...or are those read left to right also? Not sure...)....LSB on the right...