[vcf-midatlantic] portable terminal preferences

Jameel Akari jakari at bithose.com
Mon Jan 4 03:01:12 UTC 2021

As for having a dedicated terminal device… I have lusted after DEC’s handheld service terminal forever.  It’s not super practical but it’s really cool.  Same for something like a TRS-80 Model 100 or HP 200LX.

Instead, if I don't want to carry around a VT-100/320/420, then I’ve got a pile of older laptops to choose from.

Bringing us to USB-to-RS232 dongles, on which I’ll have to disagree, or at least say that your mileage may vary considerably.  If you find one that works fine for you, it really opens up your options.

The only problems I’ve ever had with USB-to-RS232 dongles has been dodgy drivers for the knock-off Prolific chips.  Actual PL-23** dongles have always worked fine for me up to 115200 baud.
(On many generations of Mac, using either ZTerm, minicom, or GNU screen, and the same on various Linuxes.)

An increasing number of modern network & datacenter equipment even comes with USB “console” ports onboard.  Just plug in a micro-USB cable to your laptop, and there’s a Prolific or FTDI on the other end ready to go.  I can run these at 57600 to 115200 all day without trouble.  These also are lovely in that if the USB cable fits, it’ll just work.  No chasing down serial cable pinout mysteries.

Now, interfacing to a vintage machine - it’s entirely possible the not-quite-in-spec voltage levels from a USB dongle could cause issues.  I know I’ve seen this happen once, but it’s been too long to remember the specifics.

If you’re doing some long-running data transfer with XMODEM and don’t have the luxury of any kind of error detection, well… I guess use what works best for you.

OTOH, a generic $10 Prolific USB dongle worked just fine on my SYM-1 at its maximum speed (4800?).

Jameel Akari

> On Jan 3, 2021, at 6:57 PM, Herb Johnson via vcf-midatlantic <vcf-midatlantic at lists.vcfed.org> wrote:
>> I'm curious what everyone else uses to connect to their various machines.
>> Straw poll? Thoughts?
> 1) use a device with a REAL RS-232 UART. Not a USB/serial dongle.
> http://www.retrotechnology.com/memship/mship_usb.html
> Here's a somewhat busy note about using a FTDI-brand TTL-to-USB dongle, on a 8-bit microcomputer to a USB based modern computer. It references some other information too. But the problem I want to call out in general, is the "layers of character flow control" section of the document.
> The problem in brief, is that a USB serial dongle has its own buffers and hardware and software handshaking. It is a microcontroller after all. It's only vaguely controlled by the modern computer with the USB driver, which may or may not have user-means to operate. Most people use these dongles with old "terminal emulators" that think THEY have a buffer and some handshaking control of a UART. The USB driver arbitrates some of that, but not always well.
> It's all too busy, and generally means a slower sustained baud rate to avoid loss of characters. And for long runs of characters (like XMODEM) you get losses anyway. I think trying to run an 8-bit micro at 19.2K baud at length, is asking for trouble. But people get obsessed about high baud-rates. And certainly it's no fun, to transfer a file and find errors, even with XMODEM and other protocols.
> So - find a computer with a real, live, UART buried in it. They still exist. And in fact, that GPD MicroPC suggested, *has* (apparently) a RS-232 port. Too fancy for me, any 1990's laptop will do. Some of them still work well. Even some post 2000 laptops and desktops have serial ports. Use those, available from any industrial dumpster.
> Regards, Herb Johnson
> -- 
> Herbert R. Johnson, New Jersey in the USA
> http://www.retrotechnology.com OR .net
> preserve, recover, restore 1970's computing
> email: hjohnson AT retrotechnology DOT com
> or try later herbjohnson AT comcast DOT net

More information about the vcf-midatlantic mailing list