So the 74x138 is pretty cool... - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: March 14, 2018, 03:24:15 am
content: I saw someone using it to mask out signals to decode addresses to memory/ROM. It essentially gives you 3 configurable inputs (you choose high or low), 2 lows, and 1 high. A very useful logic chip.Like this, what other logic chips are good to know about and can do unique things!

author: Bassman59
author_rank: Super Contributor
timestamp: March 14, 2018, 03:38:34 am
content: Quote from: alank2 on March 14, 2018, 03:24:15 amThe enable inputs are like that so you can expand the decoder from 3-to-8 to I think a one of 32 selector using no other logic chips.QuotePretty much all of the non-primitive-gate devices in the 74-series (and older CMOS 4000 family) have clever inputs like that to simplify designs. Eliminating the glue of primitive gates (AND, etc) made layout easier.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 14, 2018, 05:30:35 am
content: CD4043 -- quad R-S latch, useful for multi-level fault latching in controllersCD4047 -- multivibrator with complementary outputs (I've used it before as part of a forward converter)74LVC3G17 -- 5V tolerant triple schmitt buffer, and handy as a gate driver when you need something beefier than a regular CMOS logic output (also TinyLogic equivalents)74HC74 -- classic dual D f/f of course, use however you like74HC7014 -- hex schmitt buffer with precision threshold, great for line receivers, and analog applications where you can't be bothered to wire up a line of comparators at a fixed thresholdSpeaking of glue logic, single or few-gate models are great. 74HC1G14 and the like. Single or triple inverters/buffers, single or dual gates, single D-f/f, etc.RS422 and LVDS transceivers -- cheap comparators, the former including modest speed and usually impressive ESD capacity.CD4046 -- the original logic family PLL, and still best. Apparently they fucked up the design in the 'HC4046 (PC2 dead band, osc nonlinearity), tried to fix it twice (7046 and 9046) and never really got their head out of their ass. So, if you need good performance (at not much frequency, since it only runs at a few MHz), do go for the original.Tim

author: capt bullshot
author_rank: Super Contributor
timestamp: March 14, 2018, 07:33:30 am
content: '595 and '597 (shift registers with latch) make up super simple port expanders for microcontrollers - you can cascade them (the '595 for outputs and the '597 for inputs) and e.g. make 16 inputs and 16 outputs out of four controller pins (2x '595 and 2x '597). Use a SPI device or bit banging to serve them, I did that quite often back in the days and still sometimes today.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 14, 2018, 07:52:41 am
content: And '164 for inputs!Tim

author: Wolfram
author_rank: Frequent Contributor
timestamp: March 14, 2018, 09:08:13 am
content: On the topic of the single gate glue logic, the 74LVC1G3157 is an SPDT analog switch in SOT23-6. An excellent universal building block. This, along with the universal gates 74LVC1G57 and 74LVC1G58 allows a wide variety of logic functions to be implemented, without stocking a lot of different part numbers.

author: TerraHertz
author_rank: Super Contributor
timestamp: March 14, 2018, 10:22:52 am
content: HC125 and HCU04 are both quite useful for analog circuits.'259 is a nice way to provide 8 addressable control bits.

author: Heartbreaker
author_rank: Unknown
timestamp: March 14, 2018, 04:54:12 pm
content: Quote from: Wolfram on March 14, 2018, 09:08:13 amAlong these there is also the 1G97 and 1G98. The 1G99 even adds tri-state to its output.

author: Zero999
author_rank: Super Contributor
timestamp: March 14, 2018, 07:17:55 pm
content: The 74HCT parts are always handy for level conversion from 3.3V logic to 5V logic, especially the buffer/line driver parts. The 74HCT241 gives 8 channels and the 74HCT176 has 4 and both are tri-state, so the outputs can be disconnected, if needs be. Then there's the 74HC4050, which has 15V tolerant inputs and is useful for 5V to 3.3V translation.

author: alank2
author_rank: Super Contributor
timestamp: March 15, 2018, 03:24:54 am
content: These are all great guys!

author: ajb
author_rank: Super Contributor
timestamp: March 15, 2018, 04:02:31 am
content: Quote from: Heartbreaker on March 14, 2018, 04:54:12 pmYep, I use these all the time. There's also the CD4048, which is an interesting 8-input configurable gate, but I'm not sure there's a <5V version.

author: Zero999
author_rank: Super Contributor
timestamp: March 15, 2018, 08:55:08 am
content: Quote from: ajb on March 15, 2018, 04:02:31 amI've quickly Googled 74HC4048 and other variations, such as 74LV, LVC etc. and it doesn't exist. Like the rest of the 4000 series, the CD4048 will work at 5V and even 3V, but very slowly and with hardly any output drive.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 09:24:19 am
content: Subbed, as this infos here might be useful someday.

author: Kjelt
author_rank: Super Contributor
timestamp: March 15, 2018, 12:33:22 pm
content: 4013 dFF401xx one shot don't remember the exact part number was high at the end of the 4000 series, very usefull in the era before the cheap uCs to trigger and delay the "response" signal, could be used for many things. Always looked at it more as an analog chip than a digital one.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 15, 2018, 06:24:32 pm
content: 74xx123? CD4098 and CD4538 are other timers.Tim

author: alank2
author_rank: Super Contributor
timestamp: March 17, 2018, 06:46:22 pm
content: How do LVC and AHC logic families compare? For 5V use, is one better than the other?

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2018, 06:56:42 pm
content: Quote from: alank2 on March 17, 2018, 06:46:22 pmRead the data sheets.http://www.ti.com/lit/sg/sdyu001ab/sdyu001ab.pdfhttp://www.ti.com/lit/ml/scyb004b/scyb004b.pdfhttp://www.ti.com/lit/an/scaa034c/scaa034c.pdfhttp://www.ti.com/lit/ug/scbd152b/scbd152b.pdf

author: alank2
author_rank: Super Contributor
timestamp: March 17, 2018, 07:43:29 pm
content: Thanks for the links; I've briefly looked at the TI comparison guide. I wonder what the history is, which is newer, does one replace another, which advantages one might have over another, etc.

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2018, 10:49:30 pm
content: Quote from: alank2 on March 17, 2018, 07:43:29 pmGenerally faster, i.e. lower rise/fall time and propagation delays are better, although require more attention to layout and decoupling. As a general rule, don't use anything much faster, than you really need. If classic CD4000 logic will do then go with it, as you can often get away with poor/no decoupling and it will work on a breadboard, where the faster logic families may start to misbehave.

author: alank2
author_rank: Super Contributor
timestamp: March 17, 2018, 11:27:45 pm
content: Quote from: Hero999 on March 17, 2018, 10:49:30 pmI learned that big time with some very fast SRAM I was trying to use (10ns vs 55ns). There is another thread around here about it!

author: Howardlong
author_rank: Super Contributor
timestamp: March 18, 2018, 12:03:00 am
content: This is an interesting thread, not least because I haven’t used any traditionally based logic in any of my designs for some years, and the last time was for simple level translation.I was brought up in the 70s on 74 series TTL (straight up, none of this LS nonsense), and even some DTL, and still maintain a pretty reasonable selection of more modern variations in stock particularly in little logic versions in LVC, AUC and AUP, which are used for one-offs and jigs, but in commercial products I invariably end up engineering them out nowadays.Which is a shame, as they hold sentimental value, they are a major part of my EE career.In those days, just like the modern day Windows vs Linux and PIC vs Atmel culture wars, there was a minor TTL vs CMOS war going on, based around the perceived fragility of 4000 series compared to the power hogging but faster TTL. Of course the benefit of hindsight is that you used the best to fit the bill, based on a multitude of functional and non-functional requirements, and available skills. Plus ca change.Edit: when I was 14, I won a school book prize. ISTR the budget was about £5-£10. I chose the TTL Data Book. I am sure that tome has been on the bookshelves of many thousands of engineers, and TI still lives off its reputation, and usually these days still deserves it.