My 16f819 project to drive 2 steppers is making me crazy!!! System boots 
and runs fine sometimes. ( see below for Environment ) but only sometimes.

A slightly longer version of the story:

I was just about done on this proto board project, building a second 
neater proto board. I could not get the new one to work properly, it 
would sometimes run correctly sometimes not. Typically rebooting with 
power off and then on quickly would get it to run a stepper sequence, 
once one sequence worked others would work as well until power off.

After power on with some programed blinking of led's and response to 
pushbuttons ( all correct ) the routine often breaks down when I run a 
several hundred motor steps subroutine for the stepper.

Sometimes some of the ports bits lock up ( steppers all on portb ) 
sometimes portA outputs are also affected. MClear and a second try 
sometimes will get it to run correctly, sometimes not. As I say once it 
runs right it keeps working correctly ( with its minimal user interface 
and calls to the stepper subroutine ) until power off. Went back to old 
proto board, found same problem, but again, just sometimes. Problem 
probably had always been there but I had not paid great attention.

Environment

16f819 on Prot oboard

MPLab Assm

Great Cow Basic compile to asm.

Running on 5 volts

Using internal ossc

Full asm of shortest version of code at 
http://home.comcast.net/~russ_hensel/StepBot3asm.txt 
<http://home.comcast.net/%7Eruss_hensel/StepBot3asm.txt>

Things I have tried that have not worked:


            Improved PS decoupling, in lots of ways.

            Removed stepper loads and even the output darlingtons.

            Shadowed Port B for output, which I had not originally done.

            Removed pull down resistors on portb outputs.

            In the Great Cow Basic, moved around the routines and did 
some inspection of the asm code.

Reorganize the code in case problem was related to banking or paging.

Looked carefully for uninitialized variables.

Slowed clock down to one half mega hertz.

Turned off brown-out reset

Looked on Piclist and Google for info. including Gotchas which are great 
but do not seem to be the problem.

Tried a second 16F819

Made sure capture compare was off ( any other peripherals on PORTB That 
might be causing a problem? )

Reset pin is tied to V+ by 10 K and a .1 uF cap to ground as per manual 
( have varied the cap to higher/lower to see if this helped )

Used scope to make sure oscillator was running speed was at least 
vaguely right

Made sure low voltage programming is off

Watch dog timer is off.

Tried on off switch between power supply and chip for fast rise of power 
supply.

Have power on reset timer on.


Pretty much at my wits end, the few next steps that I have are tedious:

Pure assembler for the 819

Try with a 16F871 which I have on hand

I could supply all code etc to this list, but hope that a detailed 
examination like that will not be required. Anyone out there with a 
great insight? I feel it is something simple that I have missed.

A plea for help from Russ.




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