Thanks Chuck, yes now I'm seeing the PDF and TIFFs. I was sure they were not listed (for me) at IA a few days ago, maybe it was just a hiccup at the time. And thanks Frank, I wasn't familiar with worldcat - the nearest physical copy (for me) is about 3 hours away. Well, now I'd like to see if the words "RS-232" were uttered prior to 1969. I'll skim through some Datamation's, maybe it is mentioned there. I checked through the PDP-1 and PDP-8 manuals and don't see it referenced there. In the PDP-8 manual section 7-1 teletype and control it has "Signals transferred between the Model ASR 33 and the control logic are standard, serial, 11-unit code" (referring to mark, 8-data, and 2 stop bits). I do see "RS-232" clearly used in September 1969 Datamation (one month after the Aug 1969 standard release). September 1968 (one year earlier), pg 124 "RS 232 or MIL 188B Interface" September 1967, pg 122 "or EIA RS-232" (I'll keep searching and report on it later - unless someone is aware of some other definite earlier reference to the actual spec?) Thanks again, -Steve On Sun, Apr 20, 2025 at 12:56 AM Chuck Guzis via cctalk < cctalk(a)classiccmp.org&gt; wrote:

Ah, that 1.8GB TIF is just the cover page - scanned at 1200 DPI of mostly white! That's nuts (that it ends up at 1.8GB, isn't TIF using LZH?) But the COCR link is it (not apparent to me what COCR is referring to? but the document is what I recall coming across a while back). I scanned through the 1960s Datamations, and of the editions available (thanks to bitsavers), two notable entries: #1) 1962 March pg 58 "A Criticism of Inactivity" (in relation to "data communication"). H. E. Rennacker basically complains about the lack of data-communication standards across systems. It is insight to see the industry clearly identifies the need and benefits of doing so, while also observing that even by this time (1962) "RS-232" doesn't appear to be a fully recognized/known standard. [ my take is that the early DataSet 103A usage of pins is implicitly what RS-232 "A" would be; the earliest DataSet 103A manual I see is from 1967, even though the concept and similar equipment was probably in use a couple years earlier ] #2) The earliest complete reference to "RS-232" that I found was not until the November 1966 edition (where the entire issue is dedicated to the topic of "communications"). Note that I understand RS-232 mostly relates to electrical characteristics and form factor (with that 25-pin connector coming from Canon in the 1950s?? Then as mentioned above, the Bell DataSet effectively set the standard on which pins ought be used for what for serial communication). I also understand this is just when things were written down, in practice vendors were using all this again several years earlier (sort of like later modem compression protocols, or even later WiFi protocols -- to see if it was worth documenting, someone had to try it in "at-risk-early-adopter" product). Per regular Wikipedia on RS-232, it references " Standards for Computer Aided Manufacturing" which has this to say about RS-232A and B: ************************** 7. Standardization Status: RS-232, May 1960; RS-232-A, October 1963; RS-232-B, October 1965. RS-232-C is expected to be gradually (ten years) replaced by EIA SP-1194A (see writeup immediately below). 8. Implementation Status: Commerically, RS-232-C has enjoyed universal acceptance as the data terminal -to-modem de facto interface. Although MIL STD 188C prescribes 232-C functions, it employs different (lower voltage and lower impedance) electrical characteristics , primarily for security and privacy purposes. ******************************** Looking at the dates, it seems to me RS-232-A (if May 1960) does coincide with the DataSet 101 being more publicly known (c. 1959/1960), and RS-232-B (if Oct 1963) coincide with the DataSet 103A's release. Anyway, just poking around, no specific question here :) Wel, except a related/unrelated question -- why does MIDI use 5mA current loop? And is that why MIDI adopted the joystick port? (IBM original joystick card spec, didn't it involve measuring electrical discharge? so it is effectively a current-loop port? is that somewhat accurate?) -Steve On Sun, Apr 20, 2025 at 12:56 AM Chuck Guzis via cctalk < cctalk(a)classiccmp.org&gt; wrote:

On 4/20/25 04:11, Steve Lewis via cctalk wrote: Having occupied an adjacent building to Sequential Circuits on N. First Street, right after the orchards were bulldozed, my guess is that 5 ma was completely satisfactory for the relatively short haul that MIDI required sometime around 1980. Note that old (<Model 15) TTYs used 60 ma current loop and were strictly mechanical devices. 60 ma could adequately power the selector magnets in 1930, --Chuck

Their cite link worked for me, which led to a basically a text-file version of the following document (which is from Oct. 1976): https://archive.org/details/standardsforcom7610evan_0/page/18/mode/2up (page 18, item 7) With a blanket statement of "7. Standardization Status: RS-232, May 1960; RS-232-A, October 1963; RS-232-B," So I was just looking for more evidence to back up that statement - as in, actual copies of those standards, or other publications/products/manuals that refer to RS-232-A or RS-232-B (prior to 1969). I'm not doubting the statement! When you look at a physical Bell Model 103A, you see the DB25 connector, and its manual describing the pin usage match the modern one (pin 1 as a protective ground, pin 2 for TX, pin 3 for RX, on up to Ring Indicator as pin 22). The earliest copy of its manual I find is marked from 1967, but the ad-images are a few years earlier, and I suspect there were earlier copies of its manual (of around 1963). And as I mentioned earlier, I found Datamation talking "RS-232" as early as 1966. Just I was curious to see the actual "RS-232-A" (and B) documents, that an engineer at the time (mid-1960s) might refer to. Yes, the later -C ought to be the 3rd revision of these said docs. Per Datamation, I see some quite capable minicomputers even by 1964 (even at $30K) - if I were Joe Engineer at one of those minicomputer companies and wanted to hook my system up to a Bell DataSet 103A, would I just read the 103A's manual? Or would I seek out "RS-232-B"? Then to even know such a standard or revision existed, surely it would be mentioned/discussed in some publication (like Datamation). -Steve On Sun, Apr 20, 2025 at 12:01 PM Wayne S via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote:

I'm thinking in this case there was "industry practice." There were other competing standards/conventions, and maybe whoever was asked or decided to try to formalize whatever-the-Bell-DataSet is doing, perhaps there were draft revisions of that for a while. Or they just didn't make wide distribution, since there wasn't much need yet (early 60's few people still had computers, let alone two of them to talk to each other over a modem -- story was different towards the end of the 60's). On Sun, Apr 20, 2025 at 9:21 PM Chuck Guzis via cctalk < cctalk(a)classiccmp.org&gt; wrote:

On 4/20/25 09:18, Martin Bishop via cctalk wrote: If one asks "why current loop?", the answer is obvious. Superb induced noise immunity I think, is the big one. If you're a musician on stage with a bunch of coupled electronic gear, bear in mind that EMI due to the lighting currents themselves is an issue. It's the reason that stage mics use a shielded pair. It's also why CL is used in industrial settings. From a pre-war 19th and 20th century setting, the reason is that not only does one gain noise immunity over long (miles long) runs, but that the required current for activation can simply be adjusted at one end by varying the voltage. --Chuck

On Sun, Apr 20, 2025 at 7:36 PM Paul Koning via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: Another way to think about it : It is well-known that the (voltage) time constant in an RC circuit is given by R*C. It is less well-known that the (current) time constant in an LR circuit is L/R. So by making R as large as possible you get a low time constant, the current gets close to the final value more quickly. The receive 'magnet' (solenoid) in a Creed 7 teleprinter (more common that most Teletypes over here) will normally operate on about 12V. But if you try a 12V supply the signals are so distorted that the thing wll not print reliably. We used to use 80V with a suitable series resistor. -tony

On Sun, 20 Apr 2025, Steve Lewis wrote: Are you shure that this is not a multi-page TIFF file? Many programs have difficulties handling such files and only display the first segment. Christian

Ah, think you're right, and the Internet Archive viewer isn't a supportive viewer. Also FWIW, at the "TIA Store" if you scroll down on the RS-232 spec for "document history" then it also lists those dates of 1960 and 1963 (and 1965). <https://store.accuristech.com/standards/tia-tia-232-f?product_id=2594289> I don't see links to copies of those older revisions, so I sent them a message to ask about it (if physical copies exists and in anyway obtainable). -Steve On Tue, Apr 22, 2025 at 6:21 AM Christian Corti via cctalk < cctalk(a)classiccmp.org&gt; wrote: