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Old 09-10-2019, 20:31   #31
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Join Date: Aug 2011
Location: Petersburg, AK
Boat: Outremer 50S
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Re: Opencpn not seeing serial AIS/GPS data

I've done some playing with various software and settings. Your results make me think that the USB virtual port is expecting flow control. It shouldn't - NMEA is a streaming protocol - but it seems to be behaving that way. Here's what I checked:

By default, Hyperterminal sets CTS (along with DCD and DSR) high when it connects to a com port.

OpenCPN sets DCD and DSR high on connection but does not set CTS (not surprising, given that they're expecting a stream). If you set "Use Garmin..." in the connection definition the OpenCPN seems to toggle all three, and if you set both Garmin and "Output on this port...." then it seems to hold all three high. What I suspect is that in playing with the settings you were able to get OpenCPN to set CTS high, and the NAIS then started streaming. It's only a wild theory, but the best I can come up with.

The link Moo posted above on configuring a virtual com port is a good one. In Win 10 you can go to Device Manager, Ports, select the NAIS com port, Properties, Port Settings:

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This tab may or may not be available, it depends on the type of virtual com port driver that is created by the NAIS software. If the tab is there I would set the flow control to "None" if it isn't already.

If this was a real serial port it would be easy to jumper CTS to hold high, but in this case it may take a software solution. You may want to try any one of the software packages mentioned above that are meant to split serial/GPS signals to multiple users. They may (or may not) be programmed to set CTS high when connecting, then not worry on the output side when OpenCPN connects. That effort would be trial and error.

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