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I have a digital caliper/gauge: it works with FTDI interface and digimatic (or very similar) protocol. It is connected via usb port. I can connect it correctly, and I can read it with programs like GtkTerm or similar. I can also read the instrument via stty, but only physically pressing the button on the caliper which allows to send some signal on D+ or D- line (I don't know which one exactly....).

Is there a way (in bash for example) to send a signal on the usb lines D+ D-? The electrical specifications of the instrument says that the needed signal should be a low voltage to the "request line" for some milliseconds; which is one of the tho data lines in the usb connector, I suppose....

The tools which showed to be able to read the caliper / gauge made use of commands like DTR / RTS; can stty alone send such signals to usb ports??

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    \$\begingroup\$ You're thinking at too low a level, if it works in stty a driver for the FTDI chip will be loaded and the above sounds like standard hardware flow control. Try the stty crtscts flag that enables hardware handshaking, but otherwise you might need to post a link to a datasheet or user guide that shows exactly what's required. \$\endgroup\$ – PeterJ Feb 26 '13 at 10:16

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