> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of Olin Lathrop
> Sent: Friday, February 10, 2006 9:07 AM
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] question from someone new to the list
> 
> William Killian wrote:
> > BUT some times the game is happily chugging along and the reel
> > controller apparently loses its mind.
> 
> So the "reel controller" is the thing controlled by the PIC, not the
PC,
> right?

The little board with the PIC on it is the reel controller - sorry about
the confusion.

> 
> > It decides there was a failure
> > and the reels get sent to home positions (the going home action is a
> > slower spin so we know it is a sent home problem not a bad decision
> > about where to send them) but for some reason the reels all go to
step 0
> > with is 4 steps off of the stop for top prize.
> 
> > Okay amusing story done, does anyone know under what conditions a
PIC
> > might have trouble reading the internal EEPROM?  Design decisions in
> > making the board were some I would not have made and the programming
> > style is not one I would have used but I see no failure mode in the
code
> > that would lead to this.
> 
> There are various reasons the PIC might send the wheels to zero with
> EEPROM
> failure being only one unlikely one.

Looking more at the code it looks like it isn't EEPROM as the PIC copies
the values into RAM.  RAM seems to be always addressed by name but I am
looking for potential overwrites.

> I think the two most likely problems are noise spikes at the PIC or
> communication errors.  Try an experiment.  Let a machine run normally,
> then
> glitch the MCLR line low while the PIC is doing something without
letting
> the PC know anything happened.  All you need is a wire that you hold
one
> end
> to ground and the other end momentarily touch to the MCLR pin on the
PIC.
> You probably want to try this while the system is in various states.
What
> happens?

Gonna have to rig the board as MCLR is tied directly to 5vdc but sounds
like something to try.

> 
> Does the PIC have proper bypassing, and was proper attention paid to
the
> PIC
> ground and ground loop currents and inductive pickup paths?  You said
the
> circuit was designed by a software guy that knew a little digital
> hardware,
> so chances are the answer is "no".  This is the most likely single
cause
> of
> the problems.

I suspect that the answer is no...

> 
> The next likely cause, which may well be related to the previous, is
noise
> on the communication channel.  After reasonable electrical steps have
been
> taken, this should still be dealt with by a proper protocol that wraps
> everything in packets with checksums and performs ACK/NACK to
eventually
> guarantee reliable delivery of the data.

The protocol is bad.  Very bad.  But it does have "checksums".  Well
okay an XOR of the 3 or 5 bytes in the packets.  

> However to do anything more than speculate as above, I'd need to see
the
> schematic and board layout.  We specialize in PICs and their
surrounding
> circuitry and are all electrical engineers that understand analog.
We've
> done somewhere between 50 and 100 PIC designs, and have been gold
level
> Microchip PIC consultants for something like 6 years now.  Contact me
off
> list if you'd like professional help to look into this further.

Had a similar offer already.

Let me talk to the powers that be about getting one or both of you guys
a contract to look at this board.  Well board set since the driver chips
are on another board.  The interesting part is that they are connected
using a 50 lead ribbon with ground, 5v and 12 power supplied along that
ribbon.



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