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'[PIC]: Differences between JW and OTP parts? (16C7'
2001\03\07@085308 by D Lloyd

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Hi,

I have a friend who is complaining about the fact that he has code running
fine in a JW part that does not work in an OTP part of the same type.
I believe he is going to contact Microchip regarding this but has anyone
had experience of this? He says he has several parts, from different
batches, that are exhibiting the problem. I have not seen him programming
the parts so I cannot say whether it is a "finger trouble" problem.

Any suggestions?

Regards,
Dan

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2001\03\07@090730 by Bob Ammerman

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He needs to be sure he is initializing all RAM registers he uses. JW's often
power up with RAM clear (especially if the window is uncoverted). OTP's
seldom do.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\03\07@092405 by Olin Lathrop

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> I have a friend who is complaining about the fact that he has code running
> fine in a JW part that does not work in an OTP part of the same type.
> I believe he is going to contact Microchip regarding this but has anyone
> had experience of this? He says he has several parts, from different
> batches, that are exhibiting the problem. I have not seen him programming
> the parts so I cannot say whether it is a "finger trouble" problem.

I've only seen the reverse problem.  Ran fine on OTP but not on JW - until I
remembered to cover up the window.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, .....olinKILLspamspam@spam@embedinc.com, http://www.embedinc.com

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2001\03\07@113227 by Dipperstein, Michael

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> From: D Lloyd [.....dan.lloydKILLspamspam.....GB.ABB.COM]
> Hi,
>
> I have a friend who is complaining about the fact that he has
> code running
> fine in a JW part that does not work in an OTP part of the same type.
> I believe he is going to contact Microchip regarding this but
> has anyone
> had experience of this? He says he has several parts, from different
> batches, that are exhibiting the problem. I have not seen him
> programming
> the parts so I cannot say whether it is a "finger trouble" problem.
>
> Any suggestions?

It's been a while since I played with the JW version of the 16C74A.  If I
remember correctly, the JW part behaved more like the low voltage 16LC74A than
the 16C74A.  Your friend might have a voltage and/or operating frequency
problem.  Then again, I might just have a bad memory.

-Mike

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2001\03\07@124909 by iklas Wennerstrand

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Hi Dan,

The JW part is exactly the same as the OTP but with a window that enables
phothons to bombard memory cell to let go of their charges.
Infalling light can affect RAM registers to change so to get as near a OTP
as possible just cover the window.
Put initiations in your code that set all memory RAM to known value. In that
way all parts should behave the same.
The fact that it runs fine in a JW part can be that the code is wrong but
gets the right behavior due to infalling light.

Niklas Wennerstrand

-----Ursprungligt meddelande-----
Från: pic microcontroller discussion list [PICLISTspamspam_OUTMITVMA.MIT.EDU]
För D Lloyd
Skickat:        den 7 mars 2001 14:55
Till:   @spam@PICLISTKILLspamspamMITVMA.MIT.EDU
Ämne: [PIC]: Differences between JW and OTP parts? (16C74A)

Hi,

I have a friend who is complaining about the fact that he has code running
fine in a JW part that does not work in an OTP part of the same type.
I believe he is going to contact Microchip regarding this but has anyone
had experience of this? He says he has several parts, from different
batches, that are exhibiting the problem. I have not seen him programming
the parts so I cannot say whether it is a "finger trouble" problem.

Any suggestions?

Regards,
Dan

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2001\03\07@125533 by Charles Craft

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I never really thought about this before.

Is it true that the RAM and EPROM are on the same die which is exposed to
the window?

Guess that makes sense but just assumed that what was in the window was an
EPROM and rest of the guts were somewhere else. Does MicroChip have pictures
of the dies anywhere on their web site?

thanks
chuckc

{Original Message removed}

2001\03\07@125544 by Barry King

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> the 16C74A.  Your friend might have a voltage and/or operating frequency
> problem.

He also might have an uninitialized variable problem that works on
the JW with light shining on the RAM.  Been there.

Suggest running the jw with opaque label over the window.  That will
rule out a whole family of related things due to the silicon acting
weird when bombarded by room light.

-Barry.
------------
Barry King, Engineering Manager
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Phone: 802-482-2255
FAX:   802-482-2272

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2001\03\07@132449 by Andrew Warren

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D Lloyd <TakeThisOuTPICLISTEraseMEspamspam_OUTMITVMA.MIT.EDU> wrote:

> I have a friend who is complaining about the fact that he has code
> running fine in a JW part that does not work in an OTP part of the
> same type. I believe he is going to contact Microchip regarding
> this but has anyone had experience of this? He says he has several
> parts, from different batches, that are exhibiting the problem.

Dan:

From the answer to Question #1 on my 5-year-old Qestion-and-Answer
web page:

   http://home.netcom.com/~fastfwd/answers.html#PIC00001

   Why does my program work on a JW (Windowed EPROM) part, but not
   on an OTP part?

       Are you initializing all the file registers and the OPTION
       register?

       With the window uncovered, a JW part can clear all its File
       Registers just by being exposed to light. If you're not
       explicitly initializing RAM, this is kinda handy. If you
       cover the window, though, the JW part behaves just like the
       OTP; the File Registers all come up in unknown states and
       the code doesn't work.

Your friend is undoubtedly relying on the PIC to power up with its
RAM clear.  Microchip's documentation says that the RAM comes up in
an unknown state, so he shouldn't be making that assumption.

To convince himself that this really IS the problem, he can cover the
window of a JW part with something opaque (like black electrical
tape) and power it up.  He'll see that it fails just like an OTP
part.

To fix the problem, he should modify his code to initialize all RAM
to 0 on reset.

-Andy


=== Andrew Warren --- RemoveMEaiwspamTakeThisOuTcypress.com
=== IPD Systems Engineering, CYSD
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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2001\03\07@150501 by Bob

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The only other thing that I can think of, is that if he is using the internally
factory trimmed Oscillator, he may have forgotten to rewrite the code so that it
doesn't write to the calibration byte on the OTP's during programming (just put
a remark code in front of that retlw statement).



{Original Message removed}

2001\03\07@170148 by Barry King

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> Is it true that the RAM and EPROM are on the same die which is exposed to
> the window?

Yes.  Its a single chip.  If you look into the /JW, the largest
uniform square area is likely the EPROM, one of the other largish
squares is the RAM.

-Barry.
------------
Barry King
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Check out the accumulated (PIC) wisdom of the ages at:
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2001\03\09@043554 by D Lloyd

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part 1 1611 bytes content-type:text/plain; charset=us-ascii
Hi,

Thanks to everyone who replied to this thread - I have passed them on to my
friend. He assures me that he covered the window up when using the JW part
but it would not surprise me if he had something uninitialised
somewhere......My friend is "self-taught" (or not, as the case may be, in
the sense of never reading up on how micros/C compilers work) and does
strange things like using a goto, halfway through a function call, to go to
a label inside another function.............! (Yes, there are reasons why
this would continue to work on a PIC with his particular compiler)

Dan




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Subject:  Re: [PIC]: Differences between JW and OTP parts? (16C74A)

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> Is it true that the RAM and EPROM are on the same die which is exposed to
> the window?

Yes.  Its a single chip.  If you look into the /JW, the largest
uniform square area is likely the EPROM, one of the other largish
squares is the RAM.

-Barry.
------------
Barry King
NRG Systems "Measuring the Wind's Energy"
http://www.nrgsystems.com
Check out the accumulated (PIC) wisdom of the ages at:
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