Hi,
We don't have any onboard FTDI chip
I didn't talk about "onboard" either...
Before you just talked about a laptop and FTDI....but now I have to assume it's not the laptop that is rebooting.
You know ... any laptop has a processor inside....that may reboot.
And most probably the problem is neither related to USB nor to the FTDI chip.
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Now to the IPQ chip .... isn't it an interface chip rather than a processor?
And it seems you don't use true RS232.
Many things are not clear to me.
--> it's time for a somehow detailed drawing about your situation. All the way from laptop to target processor.
With detailed informations about signals, levels, wiring...
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Still there is a good chance for a software problem.
Disconnecting wires will cause some faulty signals .... causing timing, framing and parity errors.
Maybe just the error handling is bad.
Who designed the IPQ related hardware, who wrote the software?
Klaus