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PICList Thread
'ROM vs OTP'
1999\02\17@132907 by Jack Shidemantle

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I just rec'd the new Microchip line card. Inside they have a new
category of parts classified as "R" such as 12CR509. The only
difference they show is that the "R" version is classified as  ROM
where the others are listed as OTP/Flash. Many of course are not
flash. OTP is ROM, so what are they getting at here? Or is this just
another way to classify window parts?

Thanks
Jack Shidemantle
Automation & Development Engineer
YSI, Inc. USA

1999\02\17@135358 by jamesp

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OTP parts are really EPROM devices without a window to erase
them.  ROM parts are actually Masked ROM parts.  You have to
send your code to Microchip, and they hard code it into the
part.  The result of this is that the parts are much cheaper
than using OTP parts, if you have enough volume to justify the
initial setup costs.  Hope this helps.

                                        Regards,

                                         Jim



{Quote hidden}

1999\02\17@135607 by Gerhard Fiedler

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At 13:32 02/17/99 -0500, Jack Shidemantle wrote:
>I just rec'd the new Microchip line card. Inside they have a new
>category of parts classified as "R" such as 12CR509. The only
>difference they show is that the "R" version is classified as  ROM
>where the others are listed as OTP/Flash. Many of course are not
>flash. OTP is ROM, so what are they getting at here?

i don't know how they see it (like in marketing != technical), but
ReadOnlyMemory is not OneTimeProgrammable memory. OTP is an EPROM variety,
ROM is usually mask ROM.

ge

1999\02\17@160247 by Andy Stephenson

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OTP is PROM, which is an EPROM with no window.

The pattern 'blown' into a ROM is done with metalisation layers during the
final stages of production, which means that you have to commit to a lot of
parts.

Rgds...

...Andy

At 13:32 17/02/99 -0500, you wrote:
{Quote hidden}

1999\02\17@161104 by dave vanhorn

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At 08:25 PM 2/17/99 +0000, Andy Stephenson wrote:
>OTP is PROM, which is an EPROM with no window.
>
>The pattern 'blown' into a ROM is done with metalisation layers during the
>final stages of production, which means that you have to commit to a lot of
>parts.

They're cheap, as long as you're <SURE> your code is not going to change.
We went OTP for a while and then mask, and still ended up with a bug in one
product. It was discovered about 8 weeks after we submitted our code for a
12 week process, and had committed to 5000 chips.

Fortunately, it wasn't a huge bug.

1999\02\17@163338 by Andy Stephenson

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It's a tough break when that happens.

It's exactly why Microchip have successfull with the OTP's. They can work
out cheaper (more cost effective as Microchip would say) than going to ROM
when things like that happen. If you talk to your Microchip rep, you will
probably find that they would rather screw down the price on your OTP's in
volume rether than going mask ROM.

Motorola on the other hand, would rather go ROM than OTP.... Horses for
courses.

Temic on the 8051 types expect screw up's - they give you one free turn -
and you use it!

Rgds...

...Andy
At 16:08 17/02/99 -0500, you wrote:
{Quote hidden}

1999\02\17@174513 by Scott Shidel...

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On Wed, 17 Feb 1999, Jack Shidemantle wrote:

> I just rec'd the new Microchip line card. Inside they have a new
> category of parts classified as "R" such as 12CR509. The only
> difference they show is that the "R" version is classified as  ROM
> where the others are listed as OTP/Flash. Many of course are not
> flash. OTP is ROM, so what are they getting at here? Or is this just
> another way to classify window parts?
>
OTP and EPROM chips are essentially the same, except the OTP parts do not
have a window.  Kinda hard to erase them:)


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1999\02\17@174721 by Scott Shidel...

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On Wed, 17 Feb 1999, Mr and Mrs James Paul wrote:

>  OTP parts are really EPROM devices without a window to erase
>  them.  ROM parts are actually Masked ROM parts.  You have to
>  send your code to Microchip, and they hard code it into the
>  part.  The result of this is that the parts are much cheaper
>  than using OTP parts, if you have enough volume to justify the
>  initial setup costs.  Hope this helps.
>

What?
I thought that you could program OTPs yourself, but you just couldnt erase
it once you did.  What gives?

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1999\02\17@175927 by jamesp

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What do you mean what gives.   What you say is true.  I didn't
say anything contrary to that, did I?  If I did, I didn't mean
to.

                                          Regards,

                                            Jim


{Quote hidden}

1999\02\17@175930 by dave vanhorn

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At 05:49 PM 2/17/99 -0500, Scott Shidel... wrote:
>On Wed, 17 Feb 1999, Mr and Mrs James Paul wrote:
>
>>  OTP parts are really EPROM devices without a window to erase
>>  them.  ROM parts are actually Masked ROM parts.  You have to
>>  send your code to Microchip, and they hard code it into the
>>  part.  The result of this is that the parts are much cheaper
>>  than using OTP parts, if you have enough volume to justify the
>>  initial setup costs.  Hope this helps.
>>
>
>What?
>I thought that you could program OTPs yourself, but you just couldnt erase
>it once you did.  What gives?

Das what he said..  OTPs are windowless EPROMS, and they are more expensive
than ROM parts.

1999\02\17@180555 by Scott Shidel...

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O, I misunderstood.  I thought you were saying that OTPs HAD to be
hardcoded by Microchip, and that self programming wasnt an option.

On Wed, 17 Feb 1999, Mr and Mrs James Paul wrote:

{Quote hidden}

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1999\02\17@181135 by Derek Bischoff

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Don't feel bad.  I thought that was what he meant too.

{Quote hidden}

1999\02\17@191025 by Byron A Jeff

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>
> OTP is PROM, which is an EPROM with no window.

Actually these are not equivalent. A PROM cell has no mechanism for reversing
state once the cell has been blown. A EPROM cell can be regenerated by
exposure to UV. Even though in an OTP the EPROM is covered, nevertheless
they are EPROM cells, which are different that PROM ones....


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