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'[EE]: Logic families'
2000\06\16@222723 by Bob Ammerman

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I am afraid I am going to be showing my age by asking this question :-)

I have spent the past 25 years mostly writing code - tho' my original intent
was to be an EE!

I have been trying to get more involved in the hardware side of things
again. One thing that has bugged me lately: when I look at digital circuits
I am rather befuddled the alphabet soup that now falls between the 74 at the
beginning and the NNN at the end. My junkbox is mostly full of 74NN and
74LSNN with a little 40NN, 74HCNNN and 74HCTNNN. (Yes, I have plenty of gray
here (but at least I have plenty of hair) :-)

So:

1: where can I get a brief synopsis of the various logic families now
available.

2: what family/families are best for general purpose digital design -
especially around a PIC (this is the PICLIST!).

TIA

Bob Ammerman
RAm Systems
(high performance, high function, low level software)
[and trying to get back into the hardware business a bit!]

2000\06\16@230811 by Robert A. LaBudde

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At 10:19 PM 6/16/00 -0400, Bob wrote:
>1: where can I get a brief synopsis of the various logic families now
>available.
>
>2: what family/families are best for general purpose digital design -
>especially around a PIC (this is the PICLIST!).

The Radio-Shack commercial catalog has quite a bit of technical information
in it, including a full page comparison of digital logic families and their
specs.

I'm no heavy user, but I use the CD4xxx when I don't need speed (e.g., 1
MHz or less) and 74HCxxx when I do. The 74HCTxxx is useful when you need
tighter TTL capatability (which I normally don't) or more output current.

The advantage of the CD4xxx is the wide range of supply voltages possible.
The 74HCxxx is much narrower, although I've inadvertently run some at 15V
with no apparent harm.

Any other CMOS families besides these three have very narrow parts
functionality. The TTL families draw more power and are more voltage sensitive.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: spam_OUTralTakeThisOuTspamlcfltd.com
Least Cost Formulations, Ltd.                   URL: http://lcfltd.com/
824 Timberlake Drive                            Tel: 757-467-0954
Virginia Beach, VA 23464-3239                   Fax: 757-467-2947

"Vere scire est per causas scire"
================================================================

2000\06\16@235655 by Dan Michaels

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Bob Ammerman wrote:
........
>I have been trying to get more involved in the hardware side of things
>again. One thing that has bugged me lately: when I look at digital circuits
>I am rather befuddled the alphabet soup that now falls between the 74 at the
>beginning and the NNN at the end. My junkbox is mostly full of 74NN and
>74LSNN with a little 40NN, 74HCNNN and 74HCTNNN. (Yes, I have plenty of gray
>here (but at least I have plenty of hair) :-)
>
>So:
>
>1: where can I get a brief synopsis of the various logic families now
>available.
>
>2: what family/families are best for general purpose digital design -
>especially around a PIC (this is the PICLIST!).
>

Hi Bob, try this for a start:

"Motorola Logic Families, Which Is Best for You?
http://design.stanford.edu/spdl/logic/which_is_best.html

As Robert said, 74HC and 74HCT families are good matches with
PIC. Fast enough for any PIC, and nice low-current CMOS.

For really fast stuff, I use 74AC series. Eg, you can use several
74AC74 stages in series to divide pulserates >100 Mhz down into
something the PIC can actually see.

Also, I understand you can stick a bunch of those old 74xx and
74LSxx chips into your car tires, and increase the tread life
quite a bit.

best regards,
- Dan Michaels
Oricom Technologies
http://www.sni.net/~oricom
==========================

2000\06\17@111758 by Ann & David Scott

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Horowitz and Hill, "The Art of Electronics", 2nd ed., p570, table of Logic Families & data.  Also this table is reproduced in the
ARRL Handbook, p 24.24 (1999 ed.).  Just happened to run across this just before I read your email. :)

Dave
----- Original Message -----
From: Bob Ammerman <.....RAMMERMANKILLspamspam@spam@PRODIGY.NET>

snip

> 1: where can I get a brief synopsis of the various logic families now
> available.

2000\06\17@164519 by Oliver Broad

picon face
Bob Ammerman asked:

2: what family/families are best for general purpose digital design -
especially around a PIC (this is the PICLIST!).

I would say the 4000 and 74HC series are most usefull. Operation at extreme
speed might occasionally call for faster devices. 74HCT has some
applications.

4000 type: Readily available, low cost, contains a number of usefull analog
functions including the 4007 triple complementary pair+inverter, one of the
few devices to feature mosfets with the substrate not connected to the
source. Voltage range not a good match to the PIC, not sure whether it
would work at 3v. Slow speed can be an advantage in mixed signal circuits
as supply noise is low. 4049/4050 buffers accept inputs above the supply.

74HC: Readily available, costs more than 4000, some analog functions which
will have much lower on resistances than equivalent 4000. Faster (not
always an advantage). Supply range supposed to be 2v to 6v so exceeds PIC
in both directions.

74HCT: Variant of HC with lowered input thresholds, when powered from 5v
should accept signals from 3v logic.

Various 'low voltage logic' families have sprung up to operate from
3.0v-3.5v but a PIC circuit is unlikely to require the higher speed so 74HC
should be adequate. Some of the new devices accept inputs above the supply,
and some will even allow a tristated output to be pulled above the supply
(most CMOS will not like this).

There is also a family of digital switch devices (pass transistors) which
would be of little interest except they offer a very simple way of
interconnecting different logic levels.

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