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
In the early 70s my employer used stand alone data entry tape units in our remote locations. We started with NCR units but then switched to Tally. In the late afternoon the data would be transmitted to the home office in Chicago for processing. Also using NCR/Tally units. We used Racal-Milgo modems. These things were about the size of a large home stereo receiver. We started at 2400 baud. The units could do 3600 or 4800 (I don’t remember which) if a circuit board strap was moved.
We had locations in many cities/towns all the way out to Montana. It was decided that we needed to have the ability to switch between 2400 and the faster speed when possible. We did not want to have the locals power off the modem, open it up, remove a card and move the strap. So I got volunteered to come up with a plan.
I found a place in the modem where I could mount a switch. Luckily the modem had a sliding panel on the front so the locals would not have to open the box top. Went to our fleet garage where they had the tools I needed. I made a bunch of aluminum brackets for a tiny toggle switch. Added wires to the switch.
It was also decided that we could not trust the locals to do the switch install. So part of the plan included me going to all the locations and doing the install. I did not have a car at the time so I got a fleet car. Headed south to Kentucky then turned west. Don’t remember all the states I hit but I believe the last place I hit on the way home was Rockford. I remember being on a back road in Montana and I took a picture of my speedometer. I was doing 65. This was when there was a countrywide speed limit of 55. I can’t be limited by the Man. :)
Back at the home office we had 6 NCR/Tally machines and only 4 modems. I built a plug panel box that had everything wired to it and used telephone jack plugs to connect the Tally’s to an available modem. The box also had switches for the modem speed.
I now forget how long the whole process took. Put my DeVry AAS degree to good use. :)
