Robert,

First, a major no-no ... although your method of coding could work, you s=
hould=20
really, really, really (insert infinite loop here :-) use the definitions=
=20
from the .inc files already created by Microchip.  They're part of the MP=
LAB=20
package.  Otherwise, the code is difficult to read, and adds major source=
s of=20
errors.  Especially if, as you say, you're a programmer. :-)

That said, assuming your code compiles okay and does have the correct reg=
ister=20
addresses, if the switch were in it's unpressed state, RA1 would be "1". =
 The=20
code would loop at BEGIN and the line after that (goto BEGIN).  Now, if t=
he=20
switch were pressed, RA0 goes to "0", so the code sets PORTB to all "1"'s=
=20
which would turn on the LED, BUT...assuming the switch "bounces", as is=20
expected, RA1 would flicker between "1" and "0" for a short time.  But lo=
ng=20
enough that as it gets to KEEPON, RA1 could be at 0 and would not loop at=
=20
KEEPON.  It would go straight to clearing portB and exit.  It could also =
loop=20
at KEEPON a few times before exiting due to the same switch bounce proble=
m. =20
A few times is very fast, since the internal oscillator is 4Mhz, so you w=
ould=20
not even see the LED come on.

Quick test... try a really large capacitor at the input to RA1 (Cap +ve t=
o=20
RA1, cap -ve to gnd).  If that solves your problem then you know it's the=
=20
bounce issue.

Cheers,
-Neil




On Tuesday 10 June 2003 19:47, rrc124+@PITT.EDU scribbled:
> I can't get my inputs to work. I am using a pull up switch, have set al=
l
> pins but 1 to outputs, then tied them to ground. I am using a PIC16F628
> with the configs set to everything off/disabled except the power up tim=
er.
> I have selected the internal oscillator. I'm a programmer..not EE, so
> that's my weak point but i have been checking the circuit for 3 days an=
d
> can't find what's wrong. The chip works because i got one of those LED
> blinking things to work fine. Guys...thank you so much...it's very
> upsetting when you're just starting out and can't get the easiest thing=
 to
> work. The only odd thing i could find was that my programming software
> (WinPicProg, from Dontronics) generates a different config word then do=
es
> MPLAB with the same settings.
>
> Here is my code:
>
> TMR0            EQU             1
> OPTION_R        EQU             1
> PORTA           EQU             5
> PORTB           EQU             6
> TRISA           EQU             5
> TRISB           EQU             6
> STATUS          EQU             3
> ZEROBIT         EQU             2
> CARRY           EQU             0
> PCON            EQU             0EH
> COUNT           EQU             20H
>
>                         LIST P=3D16F628                                =
     =20
>           ;  tells which processor is use ;MPLAB generated        __CON=
FIG
> 0x3F10
>                         __CONFIG 0x3D10  ;WinPicProg generated
>
>                         org             0
>                         goto    START
>
> ; config section
>
> START                   bsf     STATUS, 5
>                         movlw   b'11111111'
>                         movwf   TRISA
>                         movlw   b'00000000'
>                         movwf   TRISB
>
>                         movlw   b'00000100'
>                         movwf   OPTION_R
>                         clrf    PCON
>
>                         bcf     STATUS, 5
>                         clrf    PORTA
>                         clrf    PORTB
>
> ; program starts now
>
> BEGIN           btfsc   PORTA, 1
>                         goto    BEGIN
>                         movlw   b'11111111'
>                         movwf   PORTB
> KEEPON          btfss   PORTA, 1
>                         goto    KEEPON
>                         clrf    PORTB
>                         goto    BEGIN
>
>                         END
>
> Here is my circuit:
>                                    GND
>
> [9V+ Battery]--[914 diode]--[7805 Volt Reg]--+
>
>                           +-----[10k Res]----+
>
>             A1/PIN 18-----+--[switch]--GND   |
>
>            Vdd/PIN 14------------------------+
>
>            Vss/PIN 05------------------------GND
>
>             B4/PIN 10--[470 Ohm Res]--[LED]--GND
>
>             B3/PIN 09--[470 Ohm Res]--[LED]--GND
>
> All other pins set as output, tied to ground. The switch part of the
> circuit allows 4.5V to A1 and when pressed drops the voltage down to 0.=
 I
> checked with my multimeter. Thank you so much everyone.
>
> E-Mail: rrc124@pitt.edu
>
> Robert Campbell

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