VT340 Emulation

Peter Corlett abuse at cabal.org.uk
Sat Jun 26 07:43:16 CDT 2021

On Fri, Jun 25, 2021 at 04:53:08PM -0600, Grant Taylor via cctalk wrote:
> On 6/25/21 2:48 AM, Peter Corlett via cctalk wrote:
>> The other is in the software layer: the standards are a mess and the
>> full gamut of serial protocols are not available and/or not implemented
>> properly.
> I can't tell if that's a USB specification problem or a problem with what
> people have executed / built (thus far).

A bit of both. The USB communications device class (CDC) is designed for
modems, and it can be hit-and-miss trying to speak to something else. Of
course, that doesn't prevent one from ignoring that standard and just
creating a bespoke USB device which happens to produce RS232, and FTDI do
just that. FTDI's devices are better than standard CDC, but that's not a
terribly high bar.

> From my naive point of view, I wonder if it would be possible to build
> some sort of USB device that has a traditional UART that has supporting
> circuitry to connect to the host over USB. -- I say this because it sounds
> like many ~> most ~> all (?) USB to RS-232 converters are doing something
> inferior.

Well, these things will contain a UART of some form, because how else could
they work? For all I know they may even incorporate an actual 16550 IP core
in the design and talk to that from its firmware, although a UART uses
bugger all gates by modern standards and you can just get an intern to
design one in a lunchbreak rather than pay for an IP core.

It doesn't seem impossible to build a decent USB-serial dongle which caters
to all of the weird and wonderful edge cases, but the market for such things
is small enough that they would be quite expensive to produce, reducing the
market further.

>> The physical connector and pinout is an irrelevance in comparison. I own
>> a soldering iron.
> LOL (literally) I love your sentiment there. I quite agree with it.

Something I'm putting off is installing a USB micro-B plug on my old iPod
whose 30 pin socket has finally given up the ghost. I could just buy a new
one, except they don't make them any more: the current device called an
"iPod" is a glorified advertising hoarding which has a usability disaster of
a media player bolted on as an afterthought.

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