Talk:Pull-up resistor

Comments

After reading this article, I'm still confused. Does the term "Pull up"/"Pull down" resistor describe a specific *type* of resistor? In that case, I'm curious about how it works, what's different about how it's built from a standard resistor, and how a given resistor might be labeled should I wish to go out and buy one. Or is it a *way of using a resistor in a circuit* to achieve a "pull up/pull down" effect? (in which case, I should be able to analyse the circuit to determine how it works, once I get better a circuit analysis. :-) )

Anyway, that's what has me confused. Clarifications would be helpful. :-) -- — Preceding unsigned comment added by 206.191.119.10 (talk) 19:30, 11 March 2015 (UTC)

After reviewing other site, I'm not sure if the picture included in this article is right. I suspect that it simply includes pull-up resistor, but there is also some irrelevant information on it.

The image shows a simple circuit using both pullup and pulldown resistors. Lunkwill 19:39, 15 March 2006 (UTC)

OK -- then what is a pull-down resister? What I mean is -- that the clarity of this article depends on another, currently nonexistent, article. (Wiki writer 17:58, 17 June 2006 (UTC))

They should both be in this article, though I don't know what best to call it. — Omegatron 01:02, 19 June 2006 (UTC)

I've been thinking about it, and I don't have any great suggestions for a title that would adequately identity both of these circuit functions. Instead -- it might must be easier to write a new article for "pull-down resister." (Wiki writer 20:49, 19 June 2006 (UTC))

Merge with Pull-down resistor?

Since a "Pull up Resistor" is very similar to a "Pull down resistor", and they are used for very similar reasons, I suggest that the two articles be merged, since they are both quite slim and repeat information between them. Can we have a quick "show of hands" as to the general opinion on this?--Wierdy1024 22:07, 7 June 2007 (UTC)

the link "See also : Pull-down resistor" is pretty much misleading since it goes back to the same page -- mike, july 3,2007

Thank you for your suggestion. When you feel an article needs improvement, please feel free to make those changes. Wikipedia is a wiki, so anyone can edit almost any article by simply following the Edit this page link at the top. The Wikipedia community encourages you to be bold in updating pages. Don't worry too much about making honest mistakes — they're likely to be found and corrected quickly. If you're not sure how editing works, check out how to edit a page, or use the sandbox to try out your editing skills. New contributors are always welcome. You don't even need to log in (although there are many reasons why you might want to). — Omegatron 16:05, 4 July 2007 (UTC

• There is nothing special about pull-up or pull-down resistors, it's just how the resistors are connected in a circuit. The voltage drop across any resistor depends on the current flowing; in a circuit, currents can change and consequently the voltages at specific points in that circuit may go up at one end of what is called a pull-up resistor, or down at one end of what is called a pull-down resistor. 70.27.152.243 (talk) 19:57, 20 July 2016 (UTC)

Why use a resistor in the first place?

I'm looking for an expert on the topic of what damage/disadvantage say using a pull up or down resistor of say zero ohms is (ie. just connect an input straight to power supply or ground). I know it works, but that it's generally considered bad proctice but why? I just ask because on a project I'm working on I could dramaticly reduce the component count by wiring everything straight high or low.--Wierdy1024 22:07, 7 June 2007 (UTC)

What? That wouldn't work. You need a resistance so that the node can be pulled in the opposite direction by a smaller effective resistance in the transistor. Pull-up resistors are very cheap and small, so getting rid of them would not save much, even if it did somehow work. — Omegatron 16:10, 4 July 2007 (UTC)

I am curious why pullups and pulldowns are recommended on modern logic families. The high gate resistance at the input, in parts like SH74LVC families is specified for the input voltage level. Older TTL inputs needed current limitation on the input, so we used to use resistors. It seems acceptable to directly tie unused inputs to Vcc or GND. An exerpt from www.interfacebus.com

"The [old] TTL emitter input logic families required the resistor, while newer TTL families may not because they could accept a higher break down voltage on the input pin [protected by Schottky diodes]. The resistor value does not change based on the protection provided, but by what the input pin requires as a valid logic level. A resistor value of 1K ohm to 5k ohms is common and should work for all logic families as a pull-up.

So determine if parts count or cost come into play with this design, are you building 3 prototypes or 10,000 units [to determine the cost and impact of the resistor]. Next determine if the resistor is really required, check the IC logic family being used, it may or may not require a pull-up resistor."

(jthargenrader Aug. 13, 2007)

An input that is pulled up to a logic 1 can be forced to logic 0 with a jumper - sometimes this is useful (for diagnostics, or setting options with jumper blocks or DIP switches), and not possible to do if the input is hard-wired to the power supply rail. --Wtshymanski 18:36, 13 August 2007 (UTC)

This youtube video explains things far better than this article, and answers several of the above questions (notable why a resistor is needed, and how to pick an appropriate one). http://www.youtube.com/watch?v=BxA7qwmY9mg --Sd4dfg2 (talk) 04:14, 26 August 2012 (UTC)

Definition

No offense Wtshymanski, but I reverted your deletion of the carefully worded content I added to the lede. For one thing, it's WP standard practice for the article's first sentence to say what a pull-up is, yet this essential definition was not only missing from the lede, it was completely missing from the article! Also, examples and applications of pull-ups cannot be used as "definitions"; their practical use is limited to conveying how, where and why pull-ups are used. I'm sure you had legitimate concerns when you deleted my contribution, but unfortunately your edit summary didn't make those concerns clear. In particular, what did you mean by "a fishing net?". And when you said "introduces jargon without adding clarity", what jargon was introduced that you feel had no value and added no clarity whatsoever? I don't claim that my work is flawless, but would you please discuss these issues here before executing another wholesale reversion? Lambtron (talk) 22:54, 26 January 2015 (UTC)

"signal net" is jargon and needlessly opaque. Why are we writing a tautology into the lead sentence? We'd be insulting the reader if we wrote "A blue house is a house] that is blue." Definition is over rated in this case. --Wtshymanski (talk) 01:04, 27 January 2015 (UTC)

If "signal net" seems "opaque" to you, why not simply replace it with something you feel is less opaque? Also, please explain why you consider the definition "a taugology", keeping in mind the obvious violation of WP:BOLDTITLE in the version you reverted to. And why do you think a reader would be "insulted" by a description of the topic? I've pointed out several valid problems in the lede and made good faith attempts to correct them, and received no feedback except blanket reversions of my work and vague explanations for those reversions. I would very much like to hear your thoughts on how we can collaborate to fix the problems and bring the article up to WP standards. Lambtron (talk) 03:45, 27 January 2015 (UTC)

"I would very much like to hear your thoughts on how we can collaborate to fix the problems and bring the article up to WP standards." There are a lot of editors around here who would like nothing more. Wtshymanski does not do collaboration with anyone and exists solely to edit war. He will even change any argument he makes on one talk page to the polar opposite in another to facilitate a different edit war. He has even done this in adjacent discussions on the same talk page. See [1] for more. Wtshymanski has had two subsequent blocks for ignoring the outcome of that RfC and is a regular fixture on the administrators' noticeboards. Good luck! DieSwartzPunkt (talk) 11:11, 28 January 2015 (UTC)

@DieSwartzPunkt: Thanks for enlightening me; you have confirmed my suspicion that the article is owned by Wtshymanski. Unfortunately it takes more than luck to "collaborate" with owners -- it involves admins and consumes time that I can more productively spend elsewhere. I hope Wtshymanski will eventually become objective about the problems in the lede and fix them, since he/she seems disinclined to allow anyone else to do that. If that should happen, please note that there are two problems in the lede that need fixing:

• The first sentence fails to define "pull-up resistor" as required by WP:BEGIN
• The first sentence uses a bold link in violation of WP:BOLDTITLE

Lambtron (talk) 14:14, 28 January 2015 (UTC)

Took out the link, but you're OK with "Pull up resistorS" being bolded? I think it reads just fine. --Wtshymanski (talk) 15:35, 28 January 2015 (UTC)

Please read WP:BOLDTITLE and WP:BEGIN carefully -- they will help you understand the issues here. Lambtron (talk) 15:59, 28 January 2015 (UTC)

Wtshymanski, I see you've fixed the WP:BOLDTITLE problem. Now would you please fix WP:BEGIN, which is a much more significant problem? I've tagged the article to bring attention to this; feel free to remove it when you add a definition. Lambtron (talk) 19:01, 28 January 2015 (UTC)

Wikipedia_talk:WikiProject_Electronics#Pull-up_resistor brought me here. I have made some changes to the lead I hope they are improvements. --Kvng (talk) 19:04, 29 March 2015 (UTC)

Avoid the open collector in the example

I'm new to digital logic and I found this a bit confusing because pull-up and pull-down resistors are associated with tri-state logic, to which the open collector seems to be an alternative. Yet the example uses PU/PD resistors in a circuit with an open collector. A better concrete example might show separate circuits containing a pull-up and pull-down resistor, and avoid the use of an open collector altogether. That way each example contains a single isolated concept. Freeman77 (talk) 03:24, 15 September 2015 (UTC)

I've moved this to the bottom as is convention on talk pages. It will also improve your chances of getting other opinions.

In my understanding, tri-state logic is implemented by effectively having complementary open-collector (or open drain) transistors as the output stage and providing a means of turning both transistors off to yield the high impedance state. That really means that the pull-up or pull-down resistors which you associate with tri-state are merely the same as would be used with a single open collector output stage.

I should point out that open-collector outputs simply aren't used without a pull-up resistor. However, a tri-state output may also be connected internally to an input - for example in a general-purpose IO connection of a microcontroller chip - where the pin is programmable as either input or output. In that case the high impedance output state is selected when the pin is used as an input and no pull-up/down resistor needs to be used.

Taking all of that into account, my opinion is that open collector outputs are fundamentally related to pull-up/down resistors and it is reasonable to make use of the concept in this article. Conversely, tri-state outputs don't always use pull-up/down resistors (another example would be connecting to a shared bus) and are the more complicated concept; I wouldn't recommend trying to replace examples using OC with ones showing tri-state. --RexxS (talk) 21:58, 15 September 2015 (UTC)