Talk:Transistor–transistor logic

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[edit] Relation to RS232?

This page doesn't explain what's the relation of TTL to RS232 in modern the modern OEM market. It just made me more confused, rather than help. It's like a history lesson for people who are already 'in-the-know'. If you were to carefully read it, you would notice it doesn't explain at all, in layman's terms, WHAT TTL is.

RS-232 is a serial communcation standard, based on signals where -12V is low (or binary 0), and 12V is high (or binary 1). RS-232 also defines timing, the way bits are formed into bytes, and other things such as handshaking. TTL, on the other hand, only defines voltage levels -- 0V for low, 5V for high. There are also standard ways of making the 0V and 5V using bipolar transistors, and standard currents which flow in various cases. There is no timing standard. So in a sense you are comparing apples and oranges. TTL is an electronic design standard, RS-232 is a communication standard.
Sometimes when discussing RS-232, people talk about "TTL levels". This just means that the circuitry is made so that it accepts 0V/5V, as well as the standard -12V/12V. Otherwise it is just normal RS-232. Most RS-232 circuitry is like this. -- Tim Starling 07:41, 25 Aug 2003 (UTC)
with relation to RS/232 TTL levels can also mean that its only 0V/5V and it needs an external tranciever chip to actually connect to a RS/232 line (PICs are like this for example) Plugwash 20:47, 1 June 2006 (UTC)

[edit] Picture

Does anyone else think a different picture would show the chips a little better? The breadboard in the present picture is hard to follow and doesn't show, in my opinion, a typical application. I'll have to shoot some pics of TTL-based things I have around the house. --Wtshymanski 20:05, 8 Apr 2005 (UTC)


Here's a picture of a TTL digital clock/calendar. Today this would be one chip powered by a coin cell. Things were different in 1979.

--Wtshymanski 20:12, 10 Apr 2005 (UTC)

Not sure where I should put this but TTL also stands for Through-the-lense which is a way that a camera can adjust the lighting/flash when used in conjuction with a mounted flash. 212.161.59.210 10:23, 26 January 2007 (UTC)John McGinty212.161.59.210 10:23, 26 January 2007 (UTC)

See the disambiguation page TTL and the article Through-the-lens. --Wtshymanski 19:57, 26 January 2007 (UTC)

[edit] Comparison

Could it be said, that

?--Arnero 17:30, 27 January 2006 (UTC)

well CMOS uses mosfets rather than bipolars but its essentially two common emmiter units built with opposite polarities of transistor wired in parallell. not sure about TTL and ECL. Plugwash 01:10, 8 February 2006 (UTC)
Actually CMOS is common Source. FETs have Sources, Gates, and Drains, Bipolars have Emitters, Bases, and Collectors. -- RTC 00:23, 18 February 2006 (UTC)
RTL uses a resistor network input stage and a common emitter output stage. DTL uses a diode/resistor network input stage and a common emitter output stage. TTL uses a common base multiple emitter input stage and a common emitter output stage (The classic TTL "totempole" output stage is actually both a common emitter and common collector output combined). ECL uses a common emitter differential amplifier input stage and a common collector output stage.
In all of these bipolar technologies the logic function is implemented in the input stage and amplification is implemented in the output stage to get adequate drive for the inputs of other gates. CMOS however can perform both the logic and amplification functions in one stage.
RTC 00:34, 18 February 2006 (UTC)

[edit] 10,000 transistors is VLSI ?

"Each "chip" contains the equivalent of a few dozen to a few hundred transistors, contrasting with early very-large-scale integration (VLSI) devices that had the equivalent of up to 10,000 transistors"

10,000 transistors does not qualify as "Early VLSI" it is not Very-Large at all. LSI means at least a thousand gates, the term VLSI implies many tens of thousands.

[edit] "TTL Trigger"

I've used devices with a "TTL Trigger" or "TTL Line". Being a software engineer, I wondered why the type of logic used mattered with respect to interface. An electrical engineer explained that this just meant it spoke in TTL-levels and that it might be 5V CMOS inside the box. Is this correct? If so, perhaps something to this effect should be in the opening paragraph? —Ben FrantzDale 19:20, 1 June 2006 (UTC)

Different logic families have different rules for levels, in particular TTL and tradtional CMOS aren't really very compatible. TTL inputs tend to overload traditional cmos (especially the old 4000 series) outputs and cmos inputs tend to have the thresholds in the wrong place for detecting a high from a TTL output. There are however logic families (for example 74HCT) that will happilly interface with both. Plugwash 20:46, 1 June 2006 (UTC)

[edit] RTL vs. TTL

I'm afraid the schematic shows an RTL, not a TTL gate circuit. Suggestion: Use the image from the German site de:Transistor-Transistor-Logik. (Please help, I don't know how to transfer it here.) --84.150.154.189 19:20, 30 July 2006 (UTC)

Nope, that's a TTL-style circuit, though with fewer transistors than a real gate would have - the multiple-emitter transistor input stage is classic. Worth checking the German illustration, of course, but often there's text stuck in the illustrations which makes them non-portable between languages. --Wtshymanski 00:51, 31 July 2006 (UTC)
Oh I see, it's only the output stage that's different, which may be irrelevant. --84.150.183.132 05:27, 31 July 2006 (UTC) (was 84.150.154.189 yesterday)
The "totem pole" output stage is nearly as classic as the multiple-emitter input, so you are correct, a better illustration would show this more typical configuration. But I've always found drawing with a mouse about as handy as drawing with a bar of soap...someone with better skills is invited to come forth. Could use the German picture, I suppose...it is better in that sense. --Wtshymanski 01:09, 1 August 2006 (UTC)

[edit] Popularity of various logic alternatives

Tho it is hinted at that there has been an evolution in technologies, I think it would be interesting to see a more explicit discussion of the changes is choices available over time maybe with some numbers attached to the trends. Production or sales numbers vs time say. There was a time that one could buy TTL chips at Radio Shack. I dont think that is the case now. Choices of technology for a given application not only include technical considerations but also availability and cost of alternatives. I presume that "programable" technologies are more and more likely choice rather than discreet technolgies such as TTL (or whatever). A discussion of this would also be helpful. --Fholson 13:50, 7 August 2006 (UTC)

Well tandy (uk branch of intertan the owners of radioshak) no longer exists but maplin afaict stock both 74LS TTL and 4000 series cmos in thier stores (thier mail order also stocks some of the 74HC and 74HCT series chips) but anyone who is remotely serious ends up turning to mail order anyway a lot of the time.
The main problem with TTL chips for glue logic functions is that all the big modern integrated circuits are CMOS based and on many of them at least some of the inputs are not TTL compatible, power consumption is also a problem.
Where performance doesn't matter a lot of people (both hobbyist and pro) are turning to software on pics, they are cheap versatile, availible in dil packages to allow easy prototyping and easy to program
Programmable logic is another option but it tends to be fairly inaccesible to hobbyists except in the form of ready built demo boards due to programming issues (on older families) and nasty packages (on newer families). Plugwash 14:14, 7 August 2006 (UTC)

[edit] Logic levels?

The text says TTL high logic level is 2 volts. I vaguely remember that value to be 2.4 volts, but I don't seem to have any of my old TTL data books around ;-( I thought this was the reason for 3.3 volt CMOS logic as opposed to 3.0 volts, as it could directly interface with TTL. Can anyone confirm this? Madhu 03:03, 30 August 2006 (UTC)

[edit] Title

Is it more proper to capitalize the initial letters of each word or not? Despite the title being "Transistor-transistor logic", the introduction uses "Transistor-Transistor Logic". I'm just hoping this inconsistency can be resolved by people who know how it should be referred. --Kamasutra 18:41, 14 September 2006 (UTC)

[edit] part numbering scheme

The Part Numbering Scheme section is useful, but I think it has a more appropriate home at the 7400 Series article. Does anyone object to my moving it there? -- Mikeblas 13:52, 21 October 2006 (UTC)

Please do! The numbering scheme was out of place in logic families and fits only a little better here (in my project-building days it seems to me there was always at least one non-74XX series TTL chip in everything). Watch for case significance in article titles - you meant of course 7400 series - darn C programmers have infected everything with spurious case significance, I bet 15% of all Wikipedia maintenance activity is due to this alone. --Wtshymanski 16:26, 21 October 2006 (UTC)

[edit] Historical question

From the History section:

The Kenbak-1, possibly the first personal computer, used TTL for its CPU instead of a microprocessor chip, which was not available in 1971. According to the inventor, the most expensive component of such a computer was memory, not the processor.

Maybe I'm reading this wrong, but I was under the assumption TTL describes a method for logic development, which could easily be used in a microprocessor. 19:31, 9 November 2006 (UTC)

TTL was mostly used for small-scale and medium-scale integrated circuits, but there may have been a few TTL microprocessors, too. I can't think of any, though, just the "slices" such as AMD's Am2900 series parts (actually, I'm not even sure those were TTL internally, but some kind of bipolar logic). TTL was generally too power hungry to make LSI chips with, which is why everything went to pMOS, then depletion-load nMOS, and then CMOS. Dicklyon 07:07, 24 June 2007 (UTC)
I think there may have been a misunderstanding.
I agree with anonymous that, using the TTL design style, a single-chip TTL microprocessor can theoretically be fabbed.
I agree with Dicklyon that it is highly unlikely such a chip was ever built -- around 1971, the biggest possible chip that could be fabbed at a reasonable cost was far to small to contain an entire microprocessor (no matter which logic family design style they tried to use); by the time chip fabs could make such a large chip, other logic design styles had made TTL design styles obsolete.
However, *lots* of computers used TTL for their CPU -- not a microprocessor (a single chip), but one or more boards full of MSI TTL chips.
I'm assuming that this Kenbak-1 was one of those computers.
Other computers with a CPU built from lots of TTL chips: PDP-15, HP 9830 (?), the original VAX, the original TV Typewriter (?), ...
(I've been told that) the PDP-8 was the most widely-sold computer in the world (of its time), and (I've been told that) most PDP-8 CPUs were built from TTL chips. ...
Even today, students in some college classes and hobbyists continue to build CPUs out of a pile of MSI chips (Wikibooks:Microprocessor_Design/Wire_Wrap) -- although recently, it seems that functionally-equivalent CMOS chips are often substituted.
Lots of other computer were built even before TTL chips were invented, such as the Apollo guidance computer built out of "4,100 ICs, each containing a single 3-input NOR logic gate ... using resistor-transistor logic (RTL)." ... and I think some computers built out of ECL chips.
Should CPUs notable to have their own Wikipedia article be listed in this article, simply because they were built from TTL?
--68.0.124.33 (talk) 06:51, 26 April 2008 (UTC)
I think it wouldn't hurt to mention which notable computers were built from TTL, as long as the info is reliably sourced. I don't think all that you've been told is correct (PDP-8, for instance, was TTL only after third generation or so). Dicklyon (talk) 16:02, 26 April 2008 (UTC)

[edit] Packaging

The terms "flat-pack" and "beam-lead chips" are not commonly known outside the industry. Therse terms should carry a link or a further explanation for the sake of the uninitiated. —The preceding unsigned comment was added by 128.6.83.118 (talk) 16:11, 11 April 2007 (UTC).

[edit] Proper punctuation: en dash

Would anyone mind very much if I were to move the page and change the text to properly punctuate the subject with an en dash? For people who know English, the hyphen here is a bit nonsensical, but transistor–transistor logic makes good sense; same with diode–transistor logic resistor–transistor logic, which are better than the nonsensical resistor-transistor logic and diode-transistor logic. What is a diode transistor, anyway? Most refs don't do it right, either, but a few do, like this one. Dicklyon 06:47, 24 June 2007 (UTC)

Here is another ref that gets it right; and another, and another, and another, and another. Other things you sometimes see are a slash, or a space. Or multiple hyphens as transistor-transistor-logic. But none of these make as much sense as using the en dash, to people used to English punctuation and publishing style. Dicklyon 06:59, 24 June 2007 (UTC)

Hearing no objection, I went ahead and did it. Dicklyon 21:02, 26 June 2007 (UTC)

[edit] Expert editing needed

I was one of the few engineers in IBM that developed most of the discreet transistor switching circuits in the late 1950's and early 1960's. I believe I am about as much of an expert as there still is. Many Wikipedia articles on digital circuits appear to have been written by second hand observers and nearly every article I viewed on the subject have major and minor errors. I am forced to go by mostly memory and I am getting old. I do believe I know where my memory fails me. I fear much of the truth is about to be lost.

If there are others that lived this history or a historian who interviewed people like me twenty years ago, or more, then they may be able to help. If anyone has access to the actual documentation of that work that would be helpful?

I hope to write something but I am not sure how to present it. The subject seems to be scattered everywhere. I am thinking I should write one article in one place and link it to the many articles in Wikipedia.

Any thoughts? Any offers of help?UPCMaker 22:27, 25 August 2007 (UTC)

Wikipedia articles look like they're written by outside observers because there is no original research at Wikipedia; everything must be referenced. If you can write something that's referenced by third-party publications and not simply a collection of your memoirs, I'd be happy to help you get it formatted and posted. -- Mikeblas 04:09, 26 August 2007 (UTC)

The main problem with this article is that it misses the point. Transistor transistor logic refers to logic gates where the inputs and outputs are both controlled by transistors. That should be the entire premise of the article. Then the original operating regions of such circuits were carried over for many decades to other circuit technologies and called the "TTL logic levels" of "TTL-compatible" standard logic families of chips such as the 7400 series. Confused editors have added an insane amount of inappropriate information to this article. Potatoswatter (talk) 00:39, 7 May 2008 (UTC)

I'm somewhat expert on this; but I'm not sure what you're getting at. Can you be more explicit about what you think is "inappropriate" information? If you'd like to add some stuff about "TTL levels" or "TTL compatible", feel free. Dicklyon (talk) 04:24, 7 May 2008 (UTC)

Well... thinking how to rewrite/reorganize, "Functions" doesn't belong at all and "Applications" probably needs more context. "Theory" should be renamed and should be the first section, since that's what defines TTL and lets the reader know what it is. "History" should be after theory but should describe the development before getting to the first few applications, and should contain no unreferenced information. Right now the article gives the false impression that TTL was invented along with the IC, which it wasn't (as is revealed by the first sentence of History, then glossed over). "Comparison" should be merged into both Theory and History and should mainly serve to explain how and when TTL gained and lost its popularity.

Unfortunately, I'm really not familiar with the specifics of the subject, so I really need to study quite a bit to know how quickly TTL supplanted RTL and DTL. I know they coexisted for a long time... and the theory section kinda hints at why it's better than DTL but again writing the article would be much easier and less risky for someone who actually used both technologies at some point. Potatoswatter (talk) 08:02, 7 May 2008 (UTC)

Doesn't sound to me like the edits you want to do require an expert, so I'm going to remove that tag. Dicklyon (talk) 14:40, 7 May 2008 (UTC)
The part about what makes TTL faster than DTL is quite technical, involving parasitic capacitances and impedences. Are you sure? Potatoswatter (talk) 04:48, 8 May 2008 (UTC)
Sure of what? That it doesn't take an expert to understand or to write such a section? Pretty sure. It sounds right as it is, but it would be much better if someone would find a source to cite and make sure it agrees. I don't think that takes an expert, either; just someone with basic electronics understanding and ability to read books. Dicklyon (talk) 04:53, 8 May 2008 (UTC)
Well, both of us fit that bill, yet we're not actually doing it ;v) . Still easier for someone who knows what's what off the bat. In any case, what the expert tag does is flag it on the Wikipedia:WikiProject Electronics project page, which really might be appropriate. Potatoswatter (talk) 07:28, 8 May 2008 (UTC)
The thing is, I've never seen calling for experts do much useful. It just discourages normal editors. But I suppose you can try it for a while. Dicklyon (talk) 14:12, 8 May 2008 (UTC)
If that's your experience, mebbe it's not a good idea. Although "normal editors" seem to have simply increased the entropy in this article. Either way, we seem to be making progress for now. Potatoswatter (talk) 16:55, 8 May 2008 (UTC)

[edit] Dominance?

Potatoswatter [inserted] the statement " Despite this, for several years RTL and DTL remained the dominant technologies." In the edit summary he claims "(... and that when it was invented, it was done independantly. In any case, the basic concept is obvious enough...)"

I see nothing obvious about what logic technology was dominant in the 1960s. How can we know how long it took TTL to become dominant (that is, if it ever was dominant). --Gerry Ashton (talk) 19:23, 8 May 2008 (UTC)

Sorry. I meant dominant in the one market segment, general purpose chips. We know that TTL was not popular until the Sylvania introduction in 1963, and probably was still gaining steam as of the TI 7400 introduction in 1966. By obvious I only meant that an emitter follower followed by a common-emitter stage is obvious. Potatoswatter (talk) 19:29, 8 May 2008 (UTC)

[edit] *STTL families actually DTL?

Several places on Wikipedia it's stated that the difference between Schottky TTL and other TTL is the presence of diode clamps on the input transistor(s). However one primary source and another secondary source I found show that the input transistors are indeed removed and replaced with Schottky diodes, making STTL, LSTTL, ALSTTL and ASTTL actually DTL families. (The evaluation/inverter transistor and several others are clamped with diodes as described. Also, the DTL pull-up resistor is replaced with a complex secondary path which varies between the families.) Before I make a drastic change, is there any really good reason to class LSTTL as TTL? Potatoswatter (talk) 21:38, 10 May 2008 (UTC)

Don't change the article that much. Though I admit I was startled when I pulled out my TI TTL Logic Data Book (1988 edition) and found that the schematic for the LS TTL NAND gate does *not* have the distinctive multiple-emitter transistor that the regular Schottky does. If Texas Instruments thinks LS TTL is TTL, then I don't think we should come to the novel conclusion that LS TTL is really DTL. If it's good enough for TI, it should be good enough for Wikipedia. I would like to know why - up until a few minutes ago I'd always thought an LS gate was the same as an S but with higher resitor values. Oh, and other logic functions like NOR, etc. are much more similar in their LS and regular TTL schematics. Comment on this difference in LS TTL, but don't call it DTL. --Wtshymanski (talk) 22:00, 10 May 2008 (UTC)
Some of the diagrams in the reference you gave do have transistors on the input, although the input is connected to the base, rather than the emitter as in traditional TTL. Also, DTL refers to a specific circuit, and the circuits in the reference are not DTL. So STTL, LSTTL, and so on, should not be called DTL. --Gerry Ashton (talk) 00:55, 11 May 2008 (UTC)
The defining characteristic of DTL that the input directly drives the base of the NAND/NOR stage through a diode, not the simple presence of any transistor on the input. The transistors on the inputs are part of a power-saving active circuit in series with DTL's passive resistor, so it isn't a fundamental modification. Potatoswatter (talk) 01:05, 11 May 2008 (UTC)
I just found a reference that says multiple diode inputs to a DTL NAND can be implemented as a multiple-emitter transistor! So when is DTL "really" TTL ? --Wtshymanski (talk) 01:52, 11 May 2008 (UTC)
The diodes are fundamentally different from a transistor. The multiple-emitter transistor is pretty much equivalent to several transistors in parallel, which some other references show in place of the multiple emitters. Where's the reference? Potatoswatter (talk) 02:01, 11 May 2008 (UTC)
The ALS NAND of fig.12 of your primary source shows an active pullup transistor in place of the passive pullup resistor of DTL. So it's certainly not right to say it's really DTL-like. But more fundamentally, it not OK to make interpretations of sources, whether primary or secondary – just report what they say. Dicklyon (talk) 01:50, 11 May 2008 (UTC)
...But the secondary source I just added (which I actually found first) does have a lengthy explanation of how it's actually DTL. And the active transistor is in series with a passive resistor, so it looks to me more like an unessential power-saving measure. Potatoswatter (talk) 02:01, 11 May 2008 (UTC)