USB Serial conversion / was Re: VT340 Emulation

Brent Hilpert bhilpert at
Sat Jun 26 16:09:19 CDT 2021

On 2021-Jun-26, at 10:15 AM, Paul Koning via cctalk wrote:
>> On Jun 26, 2021, at 11:31 AM, Tapley, Mark B. via cctalk <cctalk at> wrote:
>> At one point FTDI had a reasonably good reputation, and I own one of those devices based on that reputation. I have used it with no obvious problems connecting a TRS Color Computer 3 to an iMac G3 for a floppy-drive emulator (DriveWire on the iMac), but I think only for that application so far.
>> Are there any particular pitfalls I should watch out for with the FTDI device, when/if I can get back to working with it?
> I once bought a USB serial port device with a DE-9 connector on it, Belkin I think.  It worked somewhat.  Might have needed its own driver, which on a Mac is highly unusual.  It gave me enough trouble I set it aside.
> Since then I've bought several different flavors of the FTDI USB serial device, one RS-232, one 5 volt logic, one 3.3 volt logic (the latter two with 6-pin connectors to fit onto pin headers such as are found on the BeagleBone Black).  They have always worked flawlessly (on my Mac), at a number of data rates: 4800, 9600, 19.2k, 115k.  I'll admit I haven't needed stranger cases like 5 or 6 bit data, or exotic slow speeds.  As I mentioned, if that need arises and FTDI isn't good enough I'll have the RPico to do the job.

A couple years ago, somewhat on a whim, I checked a small number of USB-Serial converters for driving a couple of Model 28 Teletypes.

I didn't really expect anything so modern to work below 300 BPS, or do the needed 5-data/2-stop, but the teletypes were 75 BPS, which is just another in the division-of-2 series down from 19200,9600,etc.; and I was actually figuring on just using 8-bit and ensuring the later bits were 0 so they would be seen as stop bits, and take a bit of a penalty on the 28 print speed (might be a little rough/abusive on the teletype commutator start/stop though).

Sometimes, ya luck out: one of them actually worked down to 75 BPS, *and* did 5-data/2-stop.

There's no ID on the physical unit but it shows up on the system (OSX) as: 
	Product ID: 0x2303
	 Vendor ID: 0x067b  (Prolific Technology, Inc.)

(Product ID 0x2303: Prolific produces a series of PL2303x USB-Serial chips.)

It was plug-n-play on the Mac (given a terminal app program that knows to accept and perform the little-used config specs).

There are some other teletypes to get going that need slower speeds, for which I intend a solution as (Paul) suggests, bit-banging out of an RPi. The code was written some time ago, but haven't gotten around to the physical connections.

More information about the cctalk mailing list