[GreenKeys] USB to TTY (model15) interface

Mon Feb 13 10:59:16 EST 2023

Ok so I've been thinking about this problem. I wonder about a possible solution. The solution I've been thinking about was to create a kind of "audio uart." Someone could write some code (would probably have to be native windows, native mac and native linux) that creates a stub or virtual serial port device driver, like com22 or something. A terminal program on the PC (or other PC software that wants to communicate at 45 baud) would connect to this com port. 

The virtual com port device driver would take the data coming from the terminal program and generate AFSK audio tones out the computer's audio port. The virtual serial port would allow configuration to determine which audio port to use. At this point, a HAL terminal unit (or any terminal unit) could be used to either generate RS232 or high voltage loop keying. But if someone wanted a dongle that looked more like a USB-serial converter, then some Arduino or equivalent thing could be built.

To that end, someone could design a ardunio or equivalent open source hardware dongle that takes that audio from the PC and directly creates either RS232 serial or a high voltage loop keying (or both). The virtual com port software would send the AFSK at 45 baud (or any baud rate you wanted) and do things like create the stop bits as desired but as audio keying. The com port device driver could have a combination of a large buffer and/or x-on/x-off flow control.  Of course data flow in the opposite direction would also occur. Serial data going into the hardware dongle would be translated to audio tones to go into the PC. The PC's virtual com port would translate the audio tones to data for the com port to send to the running software. So from a software perspective, this looks like a comport and from a hardware perspective, after this open source hardware dongle-thingy it looks like the output of a uart at 45 baud (with a loop keyer as desired). The whole thing would be like swapping out a UART with, lets just call it an Audio UART. 

In this way we are not constrained by hardware limitations, we bypass these obsolete chips and instead directly generate (or demodulate) audio which can be done at any baud rate. Then we have choices how to deal with that audio data, either use a TU directly or use some hardware dongle that does the audio conversion. 

There are some VERY smart  hardware and software people on this list (I am not among them) who could probably make this work.

Just my 2c.

73 Eugene W2HX
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-----Original Message-----
From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> On Behalf Of John Nagle
Sent: Sunday, February 12, 2023 3:33 PM
To: greenkeys at mailman.qth.net
Subject: [GreenKeys] USB to TTY (model15) interface

On 2/12/23 11:55, greenkeys-request at mailman.qth.net wrote:
> Message: 7
> Silicon Devices has, however, a development kit where everything is 
> unlocked.? There is also a utility available to set any arbitrary baud 
> rate that is wanted. Note that you have to use the older development 
> kit.? The one with an "N" in it was "improved" in a way that no longer 
> supports 45 baud.? As far as I know, the original kits are still 
> available but I wouldn't expect them to be around forever.? I bought a 
> couple of spares.
> 
> More information on the device can be found here:
> 
> https://www.aetherltd.com/connectingusb.html
> 
> PDW

Yeah, unfortunately the CP2102N will not go down to 45 Baud.

I brought this up with SIlabs, and they put it in a tech note.

https://www.silabs.com/documents/public/application-notes/an976-cp2102-3-4-9-to-cp2102n-porting-guide.pdf

In there, SILabs writes:

The CP2102N is feature compatible with the CP2102/9, with two exceptions:
• Baud Rate Aliasing
• Line Breaks / Break Conditions
Baud Rate Aliasing is a feature that allows a device to use a pre-defined baud rate in place of a baud rate that is requested by the user.
For example, a device using Baud Rate Aliasing can be programmed to use a baud rate of 45 bps whenever 300 bps is requested.
Baud Rate Aliasing is not supported on the CP2102N.
If Baud Rate Aliasing is used in a CP2102/9 design, the CP2102N is incompatible as a replacement.

The CP2102 is now listed as "Not for New Designs".
DigiKey says they still have 44,000 available, though.

It looks like the end of the line for UART hardware which can operate at 45 baud. The future is CPU-emulated UARTs, probably.

				John Nagle

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