[cctalk] Re: RS232 - parallel modems!?

Thanks, I had forgotten about the Kaypro. Looks like it uses a "custom" 4-pin wire (one of them being 5V power). So just level-shift the TX/RX pins through a MAX232 IC and it would talk to another R-232 system at 300 baud eh? Might have to seek out a lone Kaypro keyboard to give it a try. I suspect some of the "serial style" mid-1980s IBM Model M keyboards are similar. But I'm still wondering if anyone used this concept in the late 1960s - teletypes were expensive, flipping switches was tedious, so keyboard alternates were hot items by early 70's (hence the TVT popularity). On Fri, Feb 14, 2025 at 5:28 PM Mike Stein &lt;mhs.stein(a)gmail.com&gt; wrote: > I believe that at least Kaypro used a TTL form of RS-232 for the > keyboard; in fact, ISTR using an RS M100 notebook (+/- 5V) in place of a > keyboard in distant days. > > On Fri, Feb 14, 2025 at 12:27 PM Steve Lewis via cctalk < > cctalk(a)classiccmp.org&gt; wrote: > >> Rick Bensene: >> >> > I will try to find my Xircom parallel port Modem and Ethernet adapters >> in >> > a box somewhere in my storage area and take a photo of them. If I can >> find >> > them, I’ll post a link here to the photos so those in disbelief can see >> > them. >> >> >> That'd be neat to see, if you do find the Xircom parallel modem. I've >> seen >> combo ones and their "parallel-ethernet" devices (which seem to go for >> quite a premium these days), but not the modem only. Suppose they >> weren't >> too popular, as even laptops started to have built in modems. >> >> These days, I do use an SDLPT, that lets you use SD-cards to transfer >> data >> into a system over the parallel port. I suppose that's the same general >> principle (of read/writing one full byte at a time to a device). I >> haven't measured its performance yet (but would characterize it as being >> comparable to a physical 3.5" floppy disk drive kind of performance - I >> think copying Quake took over 40 minutes, something like that; but I'd >> like >> to get more accurate about it, down to an actual bytes-per-second rate). >> Measuring that might give me an answer on how fast something like >> Laplink/Interlink cable should be able to perform. >> >> As another experiment, I'll drop that ~7MHz 16550 serial card into a 386, >> and see if I can get a 386 to push data out on RS-232 faster than 115200. >> It should, but we'll see! >> >> >> And I think I will do an RS-232 themed talk in June VCF, if a spot is >> still >> open - I think I have enough now to make it interesting. One area I'm a >> little stuck on is verifying that anyone actually did make an RS-232 >> keyboard. Even for TV Typewriter, I'm not sure if I'd characterize that >> as >> RS-232 related. And Gordon Bell integrated an ASR-33 (current loop) to >> the >> PDP-1, but might not be accurate to call that RS-232 (but can't a current >> loop based thing be adapted to voltage?). I thought the POLY-88 keyboard >> was RS-232, but it'll be awhile before I can get back to that equipment. >> >> >> -Steve >> >> >> >> On Thu, Feb 13, 2025 at 6:32 PM Rick Bensene via cctalk < >> cctalk(a)classiccmp.org&gt; wrote: >> >> > Henry wrote: >> > >> > > I remember those, and when I went searching to look for more >> information >> > on them I found something I > hadn't stumbled on before - apparently >> Xircom >> > made a parallel port Ethernet adapter. It must have >> > > been pretty painful. The parallel port wasn't a great high speed >> > interface… >> > >> > ---- >> > >> > Yes, I have one of those parallel port Ethernet devices too. But, >> > remember, back at that time, Ethernet was commonly 10Mb/Sec. I think >> that >> > 100Mb/Sec was only located in high-end datacenters and was very >> expensive. >> > For a laptop that didn’t have a PCMCIA port, and you wanted it on an >> > Ethernet network, this was an acceptable way to go. Performance wasn’t >> > great, but most of the time laptops like this were used for TELNET >> > connections to other hosts on the local network for “GREEN SCREEN” type >> > applications that ran entirely on the remote host. Performance in such >> > cases wasn’t nearly as much of a concern as it would be in the not too >> > distant future. >> > >> > I will try to find my Xircom parallel port Modem and Ethernet adapters >> in >> > a box somewhere in my storage area and take a photo of them. If I can >> find >> > them, I’ll post a link here to the photos so those in disbelief can see >> > them. >> > >> > -Rick >> > >> > >> > >> > From: Henry Bent [mailto:henry.r.bent@gmail.com] >> > Sent: Thursday, February 13, 2025 3:54 PM >> > To: General Discussion: On-Topic and Off-Topic Posts < >> > cctalk(a)classiccmp.org&gt; >> > Cc: Rick Bensene &lt;rickb(a)bensene.com&gt; >> > Subject: Re: [cctalk] Re: RS232 - parallel modems!? >> > >> >