Talk:Resistor–transistor logic

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[edit] first digital logic

Resistor-Transistor Logic may well have been the earliest form of transistorized digital logic, but most people tend to associate the term "RTL" with integrated circuits, and the first family of digital integrated circuits was Motorola's MECL family, introduced in 1962.

The fan-in limitation described is specific to RTL integrated circuits; the fan-in of discrete RTL circuits varies widely depending on the specific components used.

--Brouhaha 02:04, 14 Sep 2004 (UTC)

[edit] expert help requested: is it really RTL?

Is this really a RTL gate?
Is this really a RTL gate?
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  • Some people claim a 3-input RTL gate has 3 transistors[1].
  • Some people at first seem to claim a 3-input RTL gate has only one transistor[2].

I suspect that historically, the "3-input gate with 3 transistors" is the kind historically defined as "RTL", and the arrangement that was actually implemented. I suspect the "3-input gate with 1 transistor" view is a misunderstanding, was never actually implemented -- or if it was implemented, it wasn't called "RTL".

Could an expert clarify if a "RTL gate" always used one transistor per input, or if there were significant numbers of things built with only one transistor per gate, and that the builders actually called them "RTL gates"? --68.0.124.33 (talk) 13:47, 28 March 2008 (UTC)

Yes, all sources that I can find, going back to the 1958 3rd edition of the GE Transistor manual, show multiple-input gates using a single transistor, and a resistor per input, and call them RTL. The particular figure above, however, may not be exactly right, according to the editor who uploaded it, and he doesn't have a source for it. The base bias resistor is most often tied to a supply of the opposite polarity as the collector supply. These are usually shown with PNP and called NOR gates, but of course they can be made either way, and can be called NAND or NOR depending on how 0 and 1 are assigned to high and low voltages. Some sources: [3] [4] [5]. Dicklyon (talk) 05:52, 29 March 2008 (UTC)
Thank you very much for those links.
Oddly enough, all the sources I have handy make the opposite claim.
They say RTL always has one transistor per input.
Sources: "RTL Cookbook" by Don Lancaster (1969); [6]; [7]; [8]; [9]; [10]; [11]; [12]; [13].
The Apollo Guidance Computer article mentions "integrated circuits (ICs)... containing ... 3-input NOR gates ... made ... using resistor-transistor logic (RTL)."
Those gates had one transistor per input[14]. —Preceding unsigned comment added by 68.0.124.33 (talk) 17:58, 23 April 2008 (UTC)
While googling for more information, I came across "Q: When is RTL not really RTL? A: When it's on a chip, silly!", which seems to explain the conflict.
Dicklyon has convinced me that "one transistor per gate" was often (always?) used when building things out of discrete transistors.
However, as far as I can tell, all chips called RTL always use one transistor per input -- chips such as the MC789P (MC789F), µL914, MC724P, MC715P, MC785P, MC799B, µL900, MC790P, MC791P, MC776P, MC787P.
Perhaps we should give these 2 different logic family implementation styles distinct names.
What do you think about calling them "RTL" and "MRTL", at least in this article? Can you think of a better pair of names?
Is the difference between RTL and MRTL "notable enough" enough to warrant 2 different Wikipedia articles?
--68.0.124.33 (talk) 17:36, 23 April 2008 (UTC)

[edit] Simplified schematic

It should be emphisized that the diagram is a "Simplified schematic" and does not actually work. Someone should be able to find a "published" schematic that actually works. I can only provide a design similar to those used in early computer designs. I would hate to think that some future engineer would try to build the circuit as shown and find that he wasted his time. UPCMaker (talk) 23:02, 3 April 2008 (UTC)

Actually it's no simpler than a correct one, so I replaced it, using the NPN version of the circuits in the sources I mentioned above, which is exactly what's in the cited GE Transistor Manual. Dicklyon (talk) 03:46, 4 April 2008 (UTC)

If R1 returned to a negative supply it would then work. If R1 was removed and the transistor is silicon and the temperature is low enough the circuit might be workable but very slow turning off. If the transistor is germanium, R1 returning to a negative supply is needed to turn the transistor off. R3 and R4 can turn the transistor on without any help from R1 but R1 will make it difficult or impossible to turn the transistor off. R1 returning to a negative supply is needed to overcome base leakage and provide a low enough base voltage to assure the transistor is turned off especially with a germanium transistor which has high leakage and low base emitter voltage. UPCMaker (talk) 12:44, 4 April 2008 (UTC)

I had fixed that last night, but failed to complete my edit. Now it's done; the circuit is exactly as you say, as in all the refs. Dicklyon (talk) 15:53, 4 April 2008 (UTC)

It still looks like R1 returns to the plus supply not the negative supply??? UPCMaker (talk) 00:16, 5 April 2008 (UTC)

Are you still seeing the old picture, or is it not obvious that "V-" is intended to represent a negative supply? I didn't modify the image above, but made a new version, calling it a NOR instead of NAND, for the more usual polarity interpretation. Dicklyon (talk) 02:44, 5 April 2008 (UTC)

I was seeing the old picture but now I see the correct one. Thanks! UPCMaker (talk) 18:41, 5 April 2008 (UTC)

[edit] Shama Bano

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