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'[PIC] how to DESIGN circuits with microchip produc'
2006\10\04@170650 by stef mientki

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I wonder how you guys DESIGN circuits ?

Having a lot of trouble making a design, using the ENC28J60,
working around all the bugs in this chip,
I thought a few weeks ago I had a very good design.
It ran for weeks, without any noticeable trouble.

Until to day, a new errata appeared in my mailbox,
(about a bug in the checksum calculations)
and now I can redesign my software again :-(

I think this chip is almost a year old, and still new bugs arrive,
when will it stop?
Or should we only use components older than say 2 years ?
Is this common for uChip products ?
What other experiences are there with new uChip products.

Ok, I can appreciate that uChip gives the possibility to subscribe to
errata,
but I always hope I never get mail from them ;-)

cheers,
Stef




2006\10\04@173906 by Gerhard Fiedler

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stef mientki wrote:

> I wonder how you guys DESIGN circuits ?
>
> Having a lot of trouble making a design, using the ENC28J60, working
> around all the bugs in this chip, I thought a few weeks ago I had a very
> good design. It ran for weeks, without any noticeable trouble.
>
> Until to day, a new errata appeared in my mailbox, (about a bug in the
> checksum calculations) and now I can redesign my software again :-(

I'm not sure what you mean by "design", but in general, the design should
be flexible enough for you to be able to incorporate a few workarounds. I
guess that would be the answer to the question above :)  And as long as
it's "only" a firmware change that's necessary, it's really not worst
case... :)

> I think this chip is almost a year old, and still new bugs arrive, when
> will it stop? Or should we only use components older than say 2 years ?

Not a bad thing to consider. At least if you're up for product stability.

Gerhard

2006\10\04@181502 by Steven Howes

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> I think this chip is almost a year old, and still new bugs arrive,
> when will it stop? > Or should we only use components older than say 2 years ?
> Is this common for uChip products ?

Mistakes are made by humans, mistakes will continue to be made by humans. Complex things are more prone to mistakes. Avoid complex things, use simple things. K-I-S-S.


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(decoded 7bit)

2006\10\04@182152 by Bob Axtell

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stef mientki wrote:
{Quote hidden}

When MChip was younger, there were very few errors. There were fewer
employees, fewer
managers, etc. Now, MChip is huge, and has all the attendant problems
that being big causes.

ONE of the solutions is to NEVER design with the very latest device.
Always let the smoke
clear for a year, while all the wrinkles are ironed out. Life will go
alot smoother.

But if being a good engineer was easy, EVERYBODY would be doing it.
Welcome to the club.
I learn something new every day.

--Bob

2006\10\04@203923 by Kenneth Lumia

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> I think this chip is almost a year old, and still new bugs arrive,
> when will it stop?
> Or should we only use components older than say 2 years ?
> Is this common for uChip products ?
> What other experiences are there with new uChip products.
>

Welcome to engineering!  Designing with "bleeding edge"
parts is always fun.  One time, I had the misfortune of using
a high-speed ram chip that had a pattern sensitivity problem.  
It was a brand new part from the vendor.  They were rather
unhappy when I sent in the scope traces and failed parts.  
Shut their production down for over 5 months!  

On the other hand, older parts can also have problems.  
Vendors occasionally do "die shrinks" as technology
progresses to get more parts out of a wafer and hence
lower cost.  This of course is a new part that pretends to
be an old part.  

Then there are parts that have been around for a long time
and do to some process deviation during manufacture
non-apparent problems occur.   I won't bore you with details.

I've found that the best overall strategy is to attempt to avoid
new parts if possible, and always create designs that
have significant margin over the minimum published
specification (at least as to what is practical).  This
way, even if parts don't meet spec, your designs have
a better chance of still working correctly.  

For the software/firmware side,  downloadable or
bootloadable options are a really good idea.


Ken
_______________________________________
"Well that never happened in any of the simulations"
spam_OUTklumiaTakeThisOuTspamadelphia.net



2006\10\04@234425 by Bob Axtell

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Kenneth Lumia wrote:
{Quote hidden}

I had a product that suddenly began failing when new "HC" parts had been
dieshrunk.
The new devices were incredibly hot and very sensitive to noise. I had
to redesign
the PCB and add more bypass caps and elmininate a timing race I didn't
even know was
therre. The product had been made for 6 years without a single failure
before that. Go
figure.

--Bob

{Quote hidden}

2006\10\05@075158 by olin piclist

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Kenneth Lumia wrote:
> I've found that the best overall strategy is to attempt to avoid
> new parts if possible,

OK, so where can I source the truckload of 12AX7A to make my ethernet
MAC/PHY with time tested technology?


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Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2006\10\05@081605 by Howard Winter

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Olin,

On Thu, 5 Oct 2006 07:53:19 -0400, Olin Lathrop wrote:

> Kenneth Lumia wrote:
> > I've found that the best overall strategy is to attempt to avoid
> > new parts if possible,
>
> OK, so where can I source the truckload of 12AX7A to make my ethernet
> MAC/PHY with time tested technology?

I don't know, but I could let you have a couple of ECC81s!  :-)

There used to be a saying: "Never buy anything earlier than Version 3 from Microsoft" - perhaps "Never buy anything less than 6 months old from
Microchip"?  Or: "Always wait for the -A version"?  

Cheers,


Howard Winter
St.Albans, England


2006\10\05@084007 by Steven Howes

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> OK, so where can I source the truckload of 12AX7A to make my ethernet
> MAC/PHY with time tested technology?
>

http://www.tubedepot.com/12ax7.html

:D

2006\10\05@110322 by Kenneth Lumia

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----- Original Message -----
From: "Olin Lathrop" <olin_piclistspamKILLspamembedinc.com>

> Kenneth Lumia wrote:
>> I've found that the best overall strategy is to attempt to avoid
>> new parts if possible,
>
> OK, so where can I source the truckload of 12AX7A to make my ethernet
> MAC/PHY with time tested technology?

I didn't say you should "always avoid".  For the record,
I have a ENC28J60 / PIC18F4620 / SD Flash card
project happily running on my bench right now (designed
the hardware this past December).  

Obviously, selection of really old parts is also bad as
manufacturers can "phase 5" the parts and then you're
also up the proverbial creek.   It is also possible (probable)
that newer parts typically are more "integrated" than the
collection of older parts that can do the same function and
are therefore a less expensive solution. The problem with
brand new parts is that vendors promise availability on certain
dates, and then, after they are designed in, the schedule slips
or the production ramp up is longer than expected and the
parts go under allotment.  

Design is always a balance between risk and reward.    

Ken
________________________________________
"Well that never happened in any of the simulations"
.....klumiaKILLspamspam.....adelphia.net

2006\10\05@114630 by M. Adam Davis

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1) Design according to the needs of the project.
2) You design based on assumptions
3) Mitigate risk with planning

Does your design have a long lifetime in the field?  Are you going to
be producing your design for a long time?  Will you have to support or
maintain your design for more than a year?  Will you be refactoring
the design in a year?

Does your design have extreme cost sensitivity?  Does it have size,
power consumption,  or other needs that make a particular part more
attractive?  Does it require the use of the latest cutting-edge
technology?

Once you've determined what the requirements are, then you write down
all your assumptions, and make simple plans if that assumption fails.
If the assumption is very unlikely to fail, spend little time working
on the mitigation plan.

The following assumptions are a good set to start with, as long as
you've got a good parts qualification, design, and testing cycle:

I assume any bugs that would require a hardware design change will be
discovered during part qualification and prototyping with the dev
kits.
I assume the parts I use in the hardware design after qualification
will not have bugs that require me to redesign the hardware.
I assume that if there's a software fix required before release, the
manufacturer will supply the fix and it'll take less than a week to
integrate and fix.
I assume that we will perform thorough enough testing that any
existing bugs in the silicon will be found before release, or do not
affect us due to the design and use of our product.

When asking the question, "How do I best mitigate an assumption
failure?" the best answers are (in order):
Modify the design process such that the failure is less likely to occur.
Modify the process so that it is detected as early as possible.
Modify the design and the design process so the impact is very little.
Determine alternatives as the design progresses so changes can be made quickly.

There are other options as well.  Some companies in cost-is-no-object
time-critical projects actually have two seperate redundant teams
working on the same project.  Often I'll design the PCB to accept
several different designs, primarily for second source issues with
parts that aren't generic.  PIC is nice in that (so far) they've been
plentiful, rarely EOL a good part, and many different parts are pin
compatible, so if X isn't available I can use Y, though it may cost
more.

In the case of this ethernet chip, there is no second source, and
given that it's a rather big departure from the typical parallel bus
ethernet, and Microchip has no proven experience with ethernet, I
would wait at least a year or two after this one is officially in
production, or (better) wait for them to release the next version of
the chip (or integrate it into a PIC).  This would give enough time to
find all bugs that affect most designs, and most bugs that affect many
designs.

But that would be for an 'important' project.  For a one off I'd not
hesitate to use it primarily for simplicity and ease of use reasons -
they are more important than any minor bugs that have yet to be
discovered.

-Adam

On 10/4/06, stef mientki <EraseMEs.mientkispam_OUTspamTakeThisOuTmailbox.kun.nl> wrote:
{Quote hidden}

> -

2006\10\05@122519 by alan smith

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Ken
 On the ENC28J60 part.....any pitfalls you might want to mention?  Looking at this chip for a design, but not sure about using it yet.  Any insight would be appreciated from you or other readers (things you had to do in hardware...board layout....etc)



               
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2006\10\05@123445 by alan smith

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Guess I needed to read the whole thread...it dealt with the ENC part...
 
 But the big issue of NOT designing with the latest stuff is of course, your competitor (unless you dont have one) is going to, and beat you to market.  Ive worked at places where the data sheets are only half filled...where the pinouts on the BGA were still being defined as we were doing schematics....its a fun ride.
 
 Present design doesnt have any of that yet......

               
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2006\10\05@125251 by stef mientki

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> I didn't say you should "always avoid".  For the record,
> I have a ENC28J60 / PIC18F4620 / SD Flash card
> project happily running on my bench right now (designed
> the hardware this past December).
So either you don't use the build in checksum calculations,...
... or you don't border about errors you don't see ;-)
Stef

2006\10\05@170446 by Kenneth Lumia

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----- Original Message -----
From: "alan smith" <micro_eng2spamspam_OUTyahoo.com>

>  On the ENC28J60 part.....any pitfalls you might want to
> mention?  

All the errata!

>Looking at this chip for a design, but not sure
> about using it yet.  Any insight would be appreciated
> from you or other readers (things you had to do in
> hardware...board layout....etc)

The part is easy to use, follow the datasheet and errata.  
You should probably also look at the current version of the
TCP/IP stack to determine the I/O for the LEDs.  As I recall,
some of my projects LEDs are inverted.  It seems
somewhere along the line from the early beta stack to the
current version, they modified the polarity of the I/O going
to the LEDs.  Although they made it simple to map the
software I/O to a given project (I think a header file with a
section called "your board" is used), the polarity is encoded
elsewhere.  Having to search through the code and flip them
everytime the stack is rev'd is a pain.

Just a note about using "new" parts (for the sake of the
original thread).  I probably wouldn't use
this part for any new designs (at least the ones that use
PICs).   The 18F66J60 and its family contain both the
processor and the ethernet interface.  According to the
microchip web site, the ENC28J60 is slightly under $4.00,
the 18F66J60 is slightly under $6.00 (single qty.).  For 2 bucks
you get the processor and a smaller PCB.
If your not too worried about using something new, it is
probably the way to go.

Ken
________________________________________
"Well that never happened in any of the simulations"
@spam@klumiaKILLspamspamadelphia.net

2006\10\05@172025 by peter green

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> the 18F66J60 is slightly under $6.00 (single qty.).  For 2 bucks
> you get the processor and a smaller PCB.
> If your not too worried about using something new, it is
> probably the way to go.
be warned however that J series pics have a much lower flash endurance, that
is its very easy to kill them with development work.

add to that the fact that the chip is TQFP and either your board had better
be low enough in value that you don't mind replacing your dev unit every
month or so or you'd better be good at smd rework.


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