medha
Unable to detect connected serial devices using Circuits.UART
I have a POS machine and say several serial devices are connected like scanner to COM1 , card reader to COM2, printer to COM3 or any order, i am unable to detect so using circuits.uart
The output comes as follows :
Circuits.UART.enumerate
#=> %{"ttyS0" => %{}, "ttyS1" => %{}, "ttyS2" => %{}, "ttyS3" => %{}}
Any insight on how we could detect the devices? 
Thanks in advance
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NobbZ
Back in the days I had a printer with 9 pins that also had emulation for 7 an d 24 pins.
It’s protocol had no way to ask if it’s there or what it is. Everything you sent to the printer caused at least a moving head.
And the only command that did not cause printing but gave a response back was asking for the current mode.
So it was idiomatic to “ask” for the current mode and assume it’s the correct device if it answered with one of the 6 valid modes (7, 9, 24 pins in either text or graphical mode).
This was actually a command which started scanning on a hand scanner I had that time. And if you didn’t move the scanner within a timeout period, it actually responded with a valid printer mode. This timeout was about 15 seconds.
NobbZ
You need to look that up in the technical documentation of the device, the chapter that describes the on-the-wire-protocol.
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