16f684 Porta.2 Instability

[JDM160]

I'm having a problem with PORTA.2 on a 16F684. Even though I have disabled all external interrupts and set everything to digital I/O, I can not run portA.2 as an I/O port. As a matter of fact, any change in voltage on that pin causes erratic behavior and an apparent "reset" of the chip. By change in voltage, I mean as little as touching the pin. I can only get the chip to run stable if I tie that pin to Vdd with a resistor.

Here are my program configs:

'@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
include "modedefs.bas"

DEFINE OSC 4

OSCCON = %01010000 '2 Mhz

ANSEL = %00000000 ' all digital I/O

TRISA = %11111111 ' input pins
TRISC = %11011111 ' input pins except pwm port

T2CON = %00000110 ' enable timer 2 for PWM and set prescaler to 16

CCPR1L = %00000000 'zero duty cycle
CCP1CON = %00001100 'enable PWM, active high

PR2 = 24 '0-100 duty cycle
'@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

Have i missed a necessary configuration that will disable any peripheral components that can cause this instability? Thanks in advance!

[sayzer]

Hi JDM160,

Couple of things.

1. Your DEFINE is 4 MHz but you set your PIC to 2 MHz. You are telling Complier that you are going to use 4Mhz operation, but the PIC will be running at 2 Mhz.

2. Separately from Item 1 above, check your OSCCON.0 (bit0).
OSCCON.0=1, Internal oscillator is used for system clock.
OSCCON.0=0, Clock source defined by FOSC<2:0> of the CONFIG register.

--------------------------

[paul borgmeier]

Add

CMCON0 = 7

(see datasheet)

[BobK]

Hi JDM,

Your last sentence of the first paragraph-"I can only get the chip to run stable if I tie that pin to Vdd with a resistor."

If the pins are inputs you must pull them either hi or lo. You just can't leave them hanging there!

BobK

[JDM160]

Add

CMCON0 = 7

(see datasheet)

Isn't that the same as CMCON0 = %00000000, and isn't that the power up default values anyway? If you haven't noticed, I'm new at this :-) Thanks for any help.

About the clock issues, PBPs smallest value is 4mhz for the compiler. I have no choice on that one. The only impact for my program is my pause statements.

Also, I am setting the intoscio in the fuse configuration.

As far as having to tie inputs to ground or vdd, why is it only pin PORTA.2 that is giving me trouble?

I have a feeling it has to do with the external interrupt function on that pin, but it should be disabled by default no?

Thanks again all, your help is much appreciated.

[paul borgmeier]

CMCON0 = 0 ' Default (with most of PORTA = Analog)
CMCON0=7 ' all digital (or CMCON0 = %00000111)
Again, see datasheet (PORTA section, first highlighted box)
Let us know ...

[BobK]

Hi JDM,

It's your comments like "I can only get the chip to run stable if I tie that pin to Vdd with a resistor" that caused me to send you this comment. You give us clues to the mystery and it's up to us to guess what is going on. If you read enough posts on this forum you will see that many times the people on this forum ask for complete code listings and schematics to help us out.

Now you write "As far as having to tie inputs to ground or vdd, why is it only pin PORTA.2 that is giving me trouble?" I don't know what you have actually connected to your PIC. You are only talking about PortA.2. So when you comment about putting your finger on a pin or put a resistor to Vdd then the problem goes away, what do you think the response from us should be? You have gotten some good feedback from Paul, Sayzer, and myself as to the more common problems people have encountered with the types of comments you have made. Now it's your turn to help us out some more with a drawing of what you have going so we can help you more!

BobK