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Recommend Bypass and Bulk Capacitors for Motorola Microcontrollers

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Allan Bathe

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Jul 31, 1998, 3:00:00 AM7/31/98
to
I am looking for documentation as to the recommended bypass and bulk
decoupling capacitors for a MC68HC16 and a MC68HC332. Intel calls for
four bulk decoupling and thirty-seven for the regular Pentium. I cannot
find any bypass / decoupling information about the high-end CISC
Motorola controllers. Any information would be greatly appreciated.


Gary Helbig

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Jul 31, 1998, 3:00:00 AM7/31/98
to Allan Bathe
Allan,

I'm guessing the 332 is similar enough to the 360. What has worked
well for me is to use a ceramic bypass for each power (Vcc) pin. I
alternate 0.1uF and 0.01uF. The Vcc pin connects to the cap, and the
cap connects to the plane(s). For bulk decoupling, one or two small
aluminum should be sufficient. One at each corner is overkill.
Otherwise, you need address your supply impedance.

Gary

Paul E. Bennett

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Aug 1, 1998, 3:00:00 AM8/1/98
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In article <35C1C05E...@ceddec.com> aba...@ceddec.com "Allan Bathe"
writes:

> I am looking for documentation as to the recommended bypass and bulk
> decoupling capacitors for a MC68HC16 and a MC68HC332. Intel calls for
> four bulk decoupling and thirty-seven for the regular Pentium. I cannot
> find any bypass / decoupling information about the high-end CISC
> Motorola controllers. Any information would be greatly appreciated.

I have just scanned through the user guide for this information and note
absence of this detail. this implies that the microcontroller is fairly
immune to PSU ripple and that working out to get a well regulated and
well enough decoupled VDD rail would follow the normal rules. They have
specified maximum disruptive current pulse immunity for the chip and you
have details about clocking frequencies etc. You will probably find that
the only circuits that may be affected are the analogue inputs (if you use
them).

I note that there are a number of other publications mentioned in the user
guide and I shall be trying to obtain them from my distributor as soon as
I can.

Other publications:-
CPU16 Reference Manual - CPU16RM/AD
Advanced Microcontroller (AMCU) Literature - BR1116/D

The latter one lists supplemental information.

--
Paul E. Bennett ................... <p...@transcontech.co.uk>
Transport Control Technology Ltd. <http://www.tcontec.demon.co.uk/>
+44 (0)117-9499861 <enq...@transcontech.co.uk>
Going Forth Safely


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