Hi Ron,

Which version of the nStep? Small in a sleeve or box with buttons? With Wifi?
Does it show with an assigned port under port selector?
Do you see a /dev/tty.usbmodem* and /dev/cu.usbmodem* (on High Siera anyway).
Does it show up in 'About This Mac'->SystemReport->usb ?
You can try talking to it with something like Zterm (or other terminal app that can connect to a usb serial device).
Open ZTerm, select the device, hit a few ctrl-F's, should get an 'S' back for each hit.

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