VT340 Emulation

Paul Koning paulkoning at comcast.net
Thu Jun 24 20:00:48 CDT 2021

> On Jun 24, 2021, at 8:51 PM, Grant Taylor via cctalk <cctalk at classiccmp.org> wrote:
> On 6/22/21 9:12 AM, Ethan Dicks via cctalk wrote:
>> The OP said he meant with "real" connectors, but in my case, I've encountered strange buffering issues with USB serial dongles (since they are really block-mode devices, not character-at-a-time) and I've definitely had problems supporting lines with odd parameters (especially speeds slower than 300 baud or with 5-bits-per-char, like one would use for a Model 19 or Model 28 teletype).  The hardware UARTs on AVR processors implement those juse fine (though for "50 baud", you often have to put a slower crystal on the processor because the 16-bit divisor overflows at 16-20MHz).  The "soft serial" libraries often just hard-code 8-bit implementations.  Fine for modern stuff but I have uses for connecting to electromechanical serial devices.
> These seem like real problems, which can't be overcome by a passive physical adapter.
> These also seem like implementation problems to me.  At least more than they seem like a USB spec problem.  I naively assume that if someone wanted to produce a USB-to-Serial adapter that supported the things you're describing that they could do so.  But sadly, I believe that RoI will be on the wrong side of the demand curve.

An Arduino or something of that size can easily do a USB to serial adapter in software.  That would let you do any data rate and character length the device can so (if you use its UART) or whatever you can generate in bit-banging software.  For example, a Raspberry Pico can clearly do any rate you want, including strange slow ones or oddballs like 134.5 baud 6 bits (or is that 7 -- for the serial line 2741).  45.45 baud 5 level and some strange fractional stop bit, not quite 1.5 -- no problem.  10 bit characters (for the classic PLATO terminal to host direction) -- no problem.  


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