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'[PIC]: Found difference between 16F628 and 16F628A'
2005\08\31@092331 by Shawn Tan

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Subject: Found difference between 16F628 and 16F628A
Date: Wednesday 31 August 2005 14:07
From: Maarten Hofman <spam_OUTcashimorTakeThisOuTspamgmail.com>
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam@spam@mit.edu>

Rochester, 31 augustus 2005.
Dear all,
Yesterday I received my $12.50 JDM programmer from eBay and now I can
finally program the 16F628A (for some reason the El Cheapo can handle the
16F628, but not the 16F628A, regardless of software used). So I happily
reassembled my application for the new target, programmed the device and
used it. At first all seemed to be working fine, but then I started noticing
little glitches.
I was already aware of some differences (the 16F628A consumes less power
and uses a different programming method) and I had read in the datasheet
that the configuration bits changed, that code protection is no longer
partial, that timer 1 and the internal oscillator work differently but this
was something else.
I debugged for a while, and then I discovered that the 16F628A doesn't
allow you to read the EEPROM while it is writing to it. On the 16F628, if
you read the EEPROM while writing to it, it returns 0xFF and writes the
correct value. On the 16F628A, if you read the EEPROM while writing to it,
it returns 0xFF but also stores 0xFF into it, instead of the requested
value. This is a rather unfortunate difference, which is why I decided to
let you know.
Of course, I tested this only with two 16F628 and two 16F628A that I bought
at the same time. It might be that some 16F628 exhibit the same behaviour
and that some 16F628A don't. But it really seems like something that has
been introduced in the 16F628A.
Greetings,
Maarten Hofman.

2005\08\31@094144 by Jan-Erik Soderholm

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> From: Maarten Hofman <cashimorspamKILLspamgmail.com>

> On  the 16F628, if you read the EEPROM while
> writing to it...

Why on earth do you want to do *that* ??
Did it realy say in the non-A data sheet that
that is/was supported ?

Jan-Erik.



2005\08\31@101559 by Maarten Hofman

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>
> > On the 16F628, if you read the EEPROM while
> > writing to it...

Why on earth do you want to do *that* ??

http://jen.mosha.net/PIC/tv.html

Did it realy say in the non-A data sheet that
> that is/was supported ?

In neither datasheet does it mention anything about reading while writing to EEPROM. As there is no warning against it, I assumed it was possible.
Greetings,
Maarten Hofman.

2005\08\31@114049 by Jan-Erik Soderholm

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Maarten Hofman wrote :

> In neither datasheet does it mention anything about reading
> while writing  to EEPROM.
> As there is no warning against it, I assumed it
> was possible.

Well, the fact that reading and writing shares the
same registers, could be warning...

Jan-Erik.




'[PIC]: Found difference between 16F628 and 16F628A'
2005\09\03@152807 by Snail Instruments
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>  I debugged for a while, and then I discovered that the 16F628A doesn't
>allow you to read the EEPROM while it is writing to it. On the 16F628, if
>you read the EEPROM while writing to it, it returns 0xFF and writes the
>correct value. On the 16F628A, if you read the EEPROM while writing to it,
>it returns 0xFF but also stores 0xFF into it, instead of the requested
>value. This is a rather unfortunate difference, which is why I decided to
>let you know.

Consider reading the 16F628A errata document. It won't make you happy but
at least will explain things a bit.

Josef


2005\09\03@212508 by Maarten Hofman

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> Consider reading the 16F628A errata document. It won't make you happy but
> at least will explain things a bit.

Josef


You are right! It is a hardware bug, fixed in later revisions... Thank you for pointing that out to me. I did read the errata, but not closely enough I see.

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