4017 outputs pinout: why? - Page 1
Forum section: electronics / general

author: fmzambon
author_rank: Contributor
timestamp: June 26, 2020, 05:56:26 pm
content: Hello everyone,well, it's half a rant, half a curiosity: why the heck is the pinout of the 4017 decade counter arranged as it is? I'm talking about the ten decoded outputs, I have no issue with the inputs.I mean, I would have expected the outputs to be arranged in order, say Q0 on pin 1,Q1 on pin 2, Q2 on pin 3... Q6 on pin 7, then Q7 on either pin 9 or 11, Q8 on pin 10 and Q9 on the last remaining pin. Instead they are arranged in that order that I cannot make sense of.What's the reason for this arrangement? Is it only due to the internal chip layout or is there a reason why they are arranged like this?

author: golden_labels
author_rank: Super Contributor
timestamp: June 26, 2020, 06:03:40 pm
content: Hackaday explains. tl;dr: because of how things are placed on the die.

author: fmzambon
author_rank: Contributor
timestamp: June 26, 2020, 06:31:11 pm
content: Quote from: golden_labels on June 26, 2020, 06:03:40 pmOn the upside I had guessed right.On the downside I should have searched more before opening a new thread

author: Brumby
author_rank: Unknown
timestamp: June 27, 2020, 03:11:05 am
content: No need to apologise.Someone else will have the same question - and their looking for an answer could bring them here!

author: golden_labels
author_rank: Super Contributor
timestamp: June 27, 2020, 11:39:52 am
content: Quote from: fmzambon on June 26, 2020, 06:31:11 pmIf you searched at all, there is no need to apologize! Sometimes it’s just a matter of sending the right query and no one can be blamed for missing it among many possibilities.I knew the page not because of my superior googling skills, but due to sheer luck. Just a few days earlier I came across it while participating in a discussion tangential to IC dies photos.

author: fmzambon
author_rank: Contributor
timestamp: June 27, 2020, 02:04:27 pm
content: Well, I did search. Definitely not a super-in-depth search, but still something. Both using Google and here, using the search feature of this forum.The issue is that when searching for something like "4017 pinout <anything>", most of the results simply state what the chip pinout is.I was also thinking that, perhaps, the pinout was chosen that way because that configuration allowed one to efficiently route the outputs out in several orderings. So I was hoping to find a picture showing how one could "sort" them in several ways thanks to their clever arrangement, whereas the real answer is much more mundane. Confirmation bias, perhaps?This said, the first result containing the actual reason is not that far down the Google search results page:http://letmegooglethat.com/?q=4017+pinout+reasonThat's why I said that I should have searched better.

author: jfiresto
author_rank: Frequent Contributor
timestamp: June 27, 2020, 07:45:24 pm
content: If you are curious, RCA datasheets show the original die layouts and would have answered your question.

author: David Hess
author_rank: Super Contributor
timestamp: June 27, 2020, 11:48:41 pm
content: The one I always wondered about is why the TTL quad 2-input 7400 NAND, 7408 AND, 7432 OR, and 7486 XOR parts have their outputs oriented to the right while the 7402 NOR part has its outputs oriented to the left.Another one you might have run across is why some early dual operational amplifiers had a different pinout in SO-8 versus DIP-8. The reason was that the semiconductor die had to be rotated 90 degrees to fit in the SO-8 package. Later improved dual operational amplifiers had smaller dies so they fit with the correct orientation in the smaller packages.