No clue for what USBSER is useful today. For serial communication over RS232 (com ports) you usually take USBCOM nowadays. Depend of your special device (VENDOR/ID).
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Hi, Andi
I don't know about the protocols. The devices I was thinking about are old hardware ham radio "modems" or encoders/decoders. They generally convert audio into RS232 and vice versa. They were used for AFSK modes like Radioteletype, and PSK and other digital modes. There are software modems now, of course, but some people (like me) still like to use the old hardware modems. There were quite a lot of DOS programs for them and some Windows program up through about 98. The USB converters are a lot better than they used to be so, admittedly, there is not as much need for serial ports now although I like to keep computers that have real serial ports.