I own my entire working career to some random happenings as a kid with interfacing equipment to IBM PC clones using RS232.
As a late teenager I used to hang out at the local computer store who sold Toshiba gear. I had a knack for making cables that allowed them to connect brother printers using RS232. One day a person from the local university dropped in asking if they knew anybody who could help interface a piece of lab gear to their Toshiba PC... I got recommended.. Then I helped to write the software to do the analysis work for them... That was in about 1986.. and here we are in 2025 some 40 years later... Remember 2 to 3 3 to 2 7 to 7 4, 5 to 6 6 to 4, 5 8 to 20 And 20 to 8... And if that didn't work. Just tie those pesky handshaking inputs to their nearest output and use software handshaking 😜... Built a career on that.. I cringe a little now I understand the intent of the signals. Doug On Fri, 31 Jan 2025, 7:20 pm Steve Lewis via cctalk, <cctalk@classiccmp.org> wrote: > Hey all! So, I've found myself studying up on RS-232 this year for a few > reasons. > > I'm mulling over doing an RS232 themed talk at June VCF. Not a super > exciting topic, but I do think that RS232 has an interesting history: In > the SAGE relationship, and as a follow up to (essentially) prior telegraph > communication. > > From what I've read, "50 baud" was a kind of an initial goal to beat, since > that's what the top telegraph operators could achieve (in small burst, > probably not all day). And those operators did have to also deal with > things like start/stop "bits". Maybe it wasn't an intentional goal, but > just that it establishes why "50 baud" is generally the lowest we ever see > mentioned (or, if you go slower than that, might as well use the older > tech). > > Then 75/110/130 baud to have digital-systems interoperate with classic > mechanical teletypes. Going any faster and those systems jam up or > overheat? These weren't yet called "serial ports", so I'm not sure what a > late 50s system would even call their equipment that facilitate this data > exchange (since I'm not sure what kind of crystal-clock they even had > yet). > > Then, was it the SAGE program that demonstrated the idea of doing this kind > of data exchange across copper phone lines? That is, the idea of computers > collaborating not just in a room, but across long distances (miles)? And > doing so by using an audio tone presentation? (they settled on around > 3100MHz, which ended up translating to 300 baud? hence, that's basically > why the first digital to digital system data exchange settled on that baud > rate, which was reliable on both 50 and 60Hz power systems, and > meaningfully faster than prior 110 baud - so a good milestone to turn it > into a product, which was the Bell Model 103?). > > I couldn't find much details (like a manual) on the Bell 101 equipment > (anyone seen one or have a manual?). But I did find the Bell 103 manual - > the photo of its innards is grainy, so I don't understand how the Bell 103 > did 300 baud without a UART (and one of the pinout lines I see did run > power, so not sure if that's-yet RS232 or not; I know RS232 was evolving > right at that same time circa 1962). I've about the 1970ish TR1402 > initial DIP UART, with anything prior being an experiment (like a full > board concept by DEC). > > I know from 1962, both RS232 and ASCII standards still took maybe another > decade to really gain traction as standards (at least, from what I've > read). Getting the world to comply with any standard always takes a lot of > effort (for a practical reason of everyone still having invested in the > older tooling that was still functional). But it's interesting how those > two standards are still in use (not in their original form, but least the > 1967 revisions) - extending from Baudot.and late 1800s-tech on telegraphs. > > Does anyone know of any grocery stories using RS232 in the 1960s? I think > barcode scanning was just introduced in that era. I can just imagine a > smart grocery store owner, in the backroom programming their minicomputer > for payroll and inventory management. In FORTRAN and without a CRT? > Actually, in the 60s, I think included software would be negotiated with > the provider of the computer (well, I'm not sure how that differed between > minis and mainframes). > > I know early microcomputers used RS232 for keyboards (1974-1976 era). The > IBM PC keyboard is essentially another form of serial. > > Well, sorry for the rambling - have other RS232 related questions, but > first wanted to focus on the historical aspects (and see if I'm somewhat on > the right track at least). > > -Steve >
