[cctalk] Re: RS232 - parallel modems!?

On Feb 15, 2025, at 13:22, Mike Stein via cctalk &lt;cctalk(a)classiccmp.org&gt; wrote: In the keyboard section of the attached document there are instructions for testing with a terminal & USB>TTL RS-232 adapter. > On Sat, Feb 15, 2025 at 12:43 AM Steve Lewis &lt;lewissa78(a)gmail.com&gt; wrote: > > 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!? >>>> >>> >>