[GreenKeys] Nagle's teletype board key part nearing end of life

[John Nagle]

My USD to serial board, described here:

https://github.com/John-Nagle/ttyloopdriver

uses the SiLab CP2102 USB to serial port part.

As of March 2021, the SiLabs CP2102 USB to serial part is "not 
recommended for new designs". The "drop in replacement" CP2012N will not 
work. It will not run at speeds below 300 baud.

 From SiLabs' porting guide: "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."

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

It's become difficult to find serial devices that will run at 45 baud.
The CP2102 was one of the last. It's still available, so if you plan
to build that board, stock up now.

				John Nagle