16f88 problems

[mikey11]

Greetings,

I've written a program for the 16f88 which is behaving strangely in the circuit.

I have an initial loop which waits for a button press, the button press leaves the loop, then evaluates two other pins for high or low status (a two position switch is forcing one of the pins high, and the other low).

Depending on the status the program proceeds to a ten second timed section, or a ten minute timed section.


The behaviour is this: When power is initially applied, the pic jumps past the first wait. Even when I add a two second pause before entering the loop to evaluate the first button press.

It evaluates the two pins, and proceeds to the timed section. It is evaluating the two pins properly, and the timed sections run flawlessly.

When the timed section are complete, it goes back to the loop waiting for the start button.

Then the device operates properly.
Why would it skip the wait for button press loop on the first execution?

I have tied MCLR to vdd with a 10k resistor. I have a 10uF electrolytic smoothing out the supply which is from an lm7805 supplied by a high capacity 12v source. I have a 100nf cap between vdd and ground right at the pins.

The behaviour hasn't changed at all with these extra components in place.

I have some questions; If you state ansel = 0 does that mean the analog pins are now digital? I would like this to be the case.

I've heard that defining MCLR as an input is a mistake because you can't reprogram the pic properly thereafter. This could be the case. On the same token, I've heard that MCLR can't act as an output. So I don't know what I should do with this.

I'm using the internal oscillator.

Any Ideas? I am totally stumped, and it's for a product I'd like to demo for a group ASAP.

Mike

[mackrackit]

Can we see your code?

[mikey11]

Unfortunately I don't have it with me. When I get home I will put it up.

I'm curious if there are any events during startup which could influence my code to jump past the first loop that is waiting for the buttonpress.

Also my question about ansel = 0 and whether that makes the analog pins digital still stands.

Also the fixes I tried with power supply, and the questions about the MCLR pin are still bothering me.

As I say, I don't actually think it's the code that is the problem. I feel it's more of an odd hardware issue with the 16f88. I realize this is a pbp forum, but other people have had trouble with the 16f88 that are similar to mine, and I thought some people here may have already faced this one down.

My code size is small enough for the chip as well. Something like 500 words.

[mackrackit]

I do not have the data sheet in front of me but I do not think ansel=0 is the way to go.
Check the data sheet and read this.
http://www.picbasic.co.uk/forum/showthread.php?t=561

MCLR is not a problem when made an input. The only concern is tothe external parts if any being able to handle the higher voltage. A well placed diode will normally solve any problems.

[Archangel]

I'm curious if there are any events during startup which could influence my code to jump past the first loop that is waiting for the buttonpress.

Hi Mikey11,
The buttonpress . . . does it go high or low when pressed? What is its power off status? Any chance your PIC is seeing a buttonpress condition there ? Can you accept a delay at startup before initialising your TRIS registers ?

[languer]

You still need to post the code. It truly sounds like you have something not properly initialized. If nothing else the code will show which pins are in use and what functions those pins share.

Make sure you have CMCON = 7, as well as ANSEL = 0.

[mackrackit]

As I say, I don't actually think it's the code that is the problem. I feel it's more of an odd hardware issue with the 16f88.

So why should the OP post the code? We were told that is not the problem.