LS/HCT/etc. logic familes - Page 3

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Re: LS/HCT/etc. logic familes
On 2017-07-11 10:28, John Larkin wrote:
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Exactly. That's why I also never subscribed to the PAL/GAL craze and  
tried to dissuade other engineers from that. Many used them for mundane  
stuff such as address decoders. They did not realize that it increases  
cost by a factor of 3-5 or more, that those things guzzle power and that  
the programming causes a slew of documentation overhead and thus even  
more cost.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: LS/HCT/etc. logic familes
On 07/11/2017 02:00 PM, Joerg wrote:

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I like the 74xx151! IDK if this is common knowledge but it can be used  
to synthesize any 4 input Boolean function. Like a "pico-PAL" as it were...



Re: LS/HCT/etc. logic familes
bitrex wrote on 7/11/2017 3:41 PM:
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A college professor showed us that in a logic class just to show it was  
possible.  He seemed to think it would be rather inefficient to construct  
chips that way, lol!  I guess not many back then looked far enough ahead to  
see the day when we would have more transistors than we know what to do with.

--  

Rick C

Re: LS/HCT/etc. logic familes
On 2017-07-11 14:52, rickman wrote:
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Had the guy ever participated in an industrial chip design? Sometimes  
professors know very little about real life out there. Even during their  
often mandatory "industry work experience" phase they are often cocooned  
in some plush ivory tower where only researchers work.

The topper at my university was a professor who blurted out that we only  
have to learn all this board level analog stuff for the exam. Once we  
graduate this would all be obsolete and it would all be ICs. I had to  
suppress a major ROFL outburst but the majority of students believed  
such nonsense. Oh well, for me that meant plenty of work opportunities.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: LS/HCT/etc. logic familes
On Tuesday, July 11, 2017 at 12:41:42 PM UTC-7, bitrex wrote:
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..

You need an inverter as well if you don't have true and complement of at least one of inputs.

kevin

Re: LS/HCT/etc. logic familes
kevin93 wrote on 7/11/2017 6:08 PM:
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You either need one input inverted, or you can use a mux twice the width  
with only ones and zeros on the muxed lines.  The latter is actually how  
FPGAs use muxes for logic.  Even the ones and zeros are supplied by a small  
block of RAM so they are completely programmable.

--  

Rick C

Re: LS/HCT/etc. logic familes
On Tuesday, July 11, 2017 at 4:11:28 PM UTC-7, rickman wrote:
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I agree but the OP said any function of 4 inputs with a 74xxx151 which only has 8 inputs plus the selects and enable.

kevin

Re: LS/HCT/etc. logic familes
On Tue, 11 Jul 2017 15:41:35 -0400, bitrex

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I didn't think that was possible, because it's not. It needs another
chip.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: LS/HCT/etc. logic familes
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I learned that trick from one of Don Lancaster's books when I was about 20.
 He called it "data selector logic". It was probably the CMOS Cookbook. And
 yes, in general you need both true and complement of the fourth signal.  (
Of course you could use a 4067 and get one extra bit.) ;)

I actually used a 5-bit version in the failover logic of the first civilian
 DBS system, circa 1982.  

Cheers

Phil Hobbs

Re: LS/HCT/etc. logic familes
On 07/12/2017 12:42 AM, snipped-for-privacy@gmail.com wrote:
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I believe it's possible to get XOR/XNOR with the '151 using asynchronous  
feedback, without a race.

I'd want to prove that to be sure. ;-)

Re: LS/HCT/etc. logic familes
bitrex wrote on 7/12/2017 7:55 AM:
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Why would you need feedback?

--  

Rick C

Re: LS/HCT/etc. logic familes
On 07/12/2017 12:42 AM, snipped-for-privacy@gmail.com wrote:
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In the 1982 revision of "The TTL Cookbook" Don Lancaster wrote:

"TTL is very much mainstream and will stay that way for a very long time."

Welllllll I guess "a very long time" is up

Re: LS/HCT/etc. logic familes
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Half a century is a /very/ long time indeed!

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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Re: LS/HCT/etc. logic familes
On Tue, 11 Jul 2017 21:42:28 -0700 (PDT), snipped-for-privacy@gmail.com wrote:

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It was taught in our Junior logic design course ('73) but it was noted
that it wasn't very useful.  That is, something to note but one
probably would never find a real-life use for it.

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So someone did find a use for it.  I never did, though I kept trying.
;-)

Re: LS/HCT/etc. logic familes
On Friday, July 14, 2017 at 3:42:16 AM UTC+2, snipped-for-privacy@notreal.com wrote:
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re...  
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20. He called it "data selector logic". It was probably the CMOS Cookbook.  
And yes, in general you need both true and complement of the fourth signal.
  (Of course you could use a 4067 and get one extra bit.) ;)
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I was born in '73, thank you for making me feel young :-) (sorry, couldn't  
resist)

Re: LS/HCT/etc. logic familes
On Fri, 14 Jul 2017 01:58:32 -0700 (PDT), Klaus Kragelund

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Our youngest child was born in '72 ;-)
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: LS/HCT/etc. logic familes
On Fri, 14 Jul 2017 01:58:32 -0700 (PDT), Klaus Kragelund

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Kidz these days!   ;-)

Re: LS/HCT/etc. logic familes
On Tuesday, July 11, 2017 at 7:29:04 PM UTC+2, John Larkin wrote:
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One chip programming in the production is zero cost, only tact time is affected (longer production time)

Programs that is properly documented, well I guess you don't interact a lot with software engineers. If you compare the design journals HW guys does to that of the SW guys, it's really insignificant

Cheers

Klaus

Re: LS/HCT/etc. logic familes
On Tue, 11 Jul 2017 17:01:49 -0700 (PDT), Klaus Kragelund

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True. Most software guys don't document anything. "Just read the
code." "The latest version is in the VCS repository."


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: LS/HCT/etc. logic familes
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And everyone knows schematics are self-documenting. <g>

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
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