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'74B vs. 74A'
2000\04\08@212641 by Brian Kraut

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I just checked the M'chip site and noticed that there is a 16C74B.  I
just bought a bunch of 74A parts from FAI a few days ago.  Can anyone
tell me if there are problems with the 74A.  Did I get stuck with old
stock that they couldn't sell to anyone else?

Dan Michaels wrote:

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2000\04\08@233720 by Jim Robertson

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At 07:27 PM 4/8/00 -0400, you wrote:

The 74B parts have the BRGH = 1 bug fixed and would most likely have been
cheaper. You got less for more in all likelyhood. I would ask for their
74B price to compare.

There is a real grey area here with their ethics IMHO.

Jim


{Quote hidden}

Regards,

Jim Robertson
NEWFOUND ELECTRONICS
________________________________________
Email: spam_OUTnewfoundTakeThisOuTspampipeline.com.au
http://www.new-elect.com
MPLAB compatible PIC programmers.
________________________________________

2000\04\08@234750 by Brian Kraut

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I guess I have myself to blame.  I didn't know that there were B parts when I
ordered them and I didn't ask.  I will be sure to ask what the latest
revisions are next time.  Kind of surprises me that FAI still had A parts.  I
would think their inventory moves pretty fast.

Jim Robertson wrote:

{Quote hidden}

2000\04\09@061210 by mike

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On Sat, 8 Apr 2000 21:50:14 -0400, you wrote:

>I guess I have myself to blame.  I didn't know that there were B parts when I
>ordered them and I didn't ask.  I will be sure to ask what the latest
>revisions are next time.  Kind of surprises me that FAI still had A parts.  I
>would think their inventory moves pretty fast.
>
>Jim Robertson wrote:
>
>> At 07:27 PM 4/8/00 -0400, you wrote:
>>
>> The 74B parts have the BRGH = 1 bug fixed and would most likely have been
>> cheaper. You got less for more in all likelyhood. I would ask for their
>> 74B price to compare.
There is also a subtle change to the SSP - there's another clock
polarity control bit, also introduced on the 16C63A
{Quote hidden}

B,C etc rev. parts are usually cheaper than earlier revs as they are
normally due to a die-shrink.

Microchip are unusual in that they do make an obvious change to the
part number (i.e. the rev.letter) when changing silicon, and they
still appear to be able to supply earlier versions - the 5x series is
at rev.C but I still see the old -XT etc. versions in catalogues.
I don't know of any other maker that does this, and they should be
loudly praised for it.  
There shouldn't normally be any problem using later parts in old
designs, unles you're bending the specs, but it's nice to know that
you won't suddenly find out the hard way that they've changed the
silicon without telling you!

2000\04\09@133632 by Mark Newland

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For those of us that own a Mathias, Tech-tools is coming out with a new
module soon that will allow use of the PIC16C62-65/72-74 family as well as
the PIC16C66/67/76/77 family.  These are two seperate modules now.  The one
thing that I know is that the current PIC16C62-65/72-74 module will allow the
use of the C74 and C74A but not the C74B.  The new module will allow the use
of the C74 and C74B but not the C74A.  Jerry from tech-tools told me what the
difference was but I forgot what it is (old age I guess).

Jim Robertson wrote:

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2000\04\09@181204 by Harold Hallikainen

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       I've got one board where the oscillator works with 74A parts, but not
74B. This is using a muRata resonator with built-in capacitors running at
16 MHz. On all my boards, I have very short traces from the oscillator
pins to the resonator, which is right next to the chip. On one board, I
decided to make the traces a bit wider (I think 50 mils instead of my
normal 12 mils). Worked fine 'til 74B chips started showing up! All our
other boards are using 12 mil traces and the transition to 74B went
fine...  The board has been redesigned (and we're moving to the 18c452),
but we continue to buy 74A chips 'til we run out of boards.
       It's always something!

Harold

On Sat, 8 Apr 2000 21:50:14 -0400 Brian Kraut <.....engaltKILLspamspam.....EARTHLINK.NET>
writes:
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2000\04\10@011312 by Dan Michaels

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Brian Kraut wrote:
>I just checked the M'chip site and noticed that there is a 16C74B.  I
>just bought a bunch of 74A parts from FAI a few days ago.  Can anyone
>tell me if there are problems with the 74A.  Did I get stuck with old
>stock that they couldn't sell to anyone else?
>
.....
>I guess I have myself to blame.  I didn't know that there were B parts when I
>ordered them and I didn't ask.  I will be sure to ask what the latest
>revisions are next time.  Kind of surprises me that FAI still had A parts.  I
>would think their inventory moves pretty fast.
>

Digikey currently sells both '74A and '74B, so I wouldn't think it
is an "old stock" issue. Also, you might check Arrow next time
you buy - good prices in quantity.
================

Harold Hallikainen wrote:
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Now this *IS* unfortunate, but I wonder if it isn't something to do
with using a resonator. I personally never had much luck with PIC
chips and 16 - 20 Mhz resonators myself [but I admit I didn't try
too hard, just went to a xtal].

But I'll bet the '74B chips will certainly work fine with a xtal
instead of the resonator. Plus save a little $$$ over '74A. [but
may have to solder caps on the bottom].

2000\04\11@141620 by Dwayne Reid

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<x-flowed>At 07:27 PM 4/8/00 -0400, Brian Kraut wrote:
>I just checked the M'chip site and noticed that there is a 16C74B.  I
>just bought a bunch of 74A parts from FAI a few days ago.  Can anyone
>tell me if there are problems with the 74A.  Did I get stuck with old
>stock that they couldn't sell to anyone else?

Not necessarily the case - many customers specifically require the 'A
version.

But *you* should have bought the 'B version - they should be cheaper than
the 'A version and they do not have the BRGH bug that the '74 and '74A
chips have.

Check with FAI - they may be able to work something out.

dwayne



Dwayne Reid   <dwaynerspamspam_OUTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 16 years of Engineering Innovation (1984 - 2000)

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'74B vs. 74A'
2000\05\22@103344 by Larry G. Nelson Sr.
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While the B rev part is usually cheaper and has fixes to the errata you
still need to be careful when changing to the newer silicon. You may find
the oscillator startup has changed and you may need to change your cap
values on the crystal. You may also see a slightly narrower voltage rating
as higher voltages are harder with smaller geometries. Another thing is the
robustness. Sometimes we tend to run beyond the ratings and I have seen
some of the older revisions prior to die shrinks that seem to run fine
beyond published specs where the newer die shrink can't be pushed as far.
Always test the new silicon in your application. If you obey the rules and
stay within the data sheet specifications you probably won't have problems.

Larry



At 09:50 PM 4/8/00 -0400, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
KILLspamL.NelsonKILLspamspamieee.org
http://www.ultranet.com/~nr

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