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Old 28-08-2010, 01:30   #1
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AIS Interface

Hi Everyone,
I am using a Nasa AIS Engine with a Serial to USB adapter to connect to a Usb port on my laptop which is running Opencpn. When I select the Port in the AIS tab in Tools the AIS Icon shows ok but no targets are seen on Opencpn.
This Receiver works perfectly with Shipplotter.
Am I doing something silly???
Can anyone help Please.

De Wadden
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Old 28-08-2010, 02:25   #2
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Have you checked the parameters of the virtual com port in Windows hardware manager?
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Old 28-08-2010, 03:53   #3
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Hi CarCode,
All settings are the same as on the machine that runs Shipplotter.
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Old 28-08-2010, 04:32   #4
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Quote:
Originally Posted by De Wadden View Post
Hi Everyone,
I am using a Nasa AIS Engine with a Serial to USB adapter to connect to a Usb port on my laptop which is running Opencpn. When I select the Port in the AIS tab in Tools the AIS Icon shows ok but no targets are seen on Opencpn.
This Receiver works perfectly with Shipplotter.
Am I doing something silly???
Can anyone help Please.

De Wadden
Not familiar with Opencpn but assume you have set this prog to receive AIS NMEA data on the COM port that your USB adaptor creates, & that it is set to receive on 38400 baud. It does sound like this is set ok though as you are getting the valid AIS data icon, so assume there must be an incorrect display setting, especially as it works ok with your other prog.

Note that static AIS data can take up to six minutes to appear especially with the NASA unit as it has only a switching single channel receiver.
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Old 28-08-2010, 04:34   #5
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Quote:
Originally Posted by CarCode View Post
Have you checked the parameters of the virtual com port in Windows hardware manager?
They will be set by the connected application
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Old 28-08-2010, 05:23   #6
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Quote:
Originally Posted by richardhula View Post
They will be set by the connected application
This might be true for most applications. However I got running my NMEA devices with OCPN only when set to 4800 baud 8N1.
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Old 28-08-2010, 10:11   #7
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Quote:
Originally Posted by CarCode View Post
This might be true for most applications. However I got running my NMEA devices with OCPN only when set to 4800 baud 8N1.
Hmm that's got me thinking maybe OCPN is not using correct Windows coding & requires the kickstart you suggest. Wonder if De Wadden has tried changing the COM port speed in Device Manager to 38400 baud as you suggest?

BTW COM ports derived from USB adapters are not virtual since they use hardware & provide a physical COM port.

Virtual ports are just that, created by virtual port drivers within the PC & usually associated with a program that allows data echo/sharing. Each program requiring the data connects to its own virtual port as if it were a physical one.

On the PRO side such ports are not constrained by speed. The receiving prog can set baud rate as high as it likes.

The CON is that the COM port is not usually listed in Device Manager which can fool some badly written progs. You can manually create an entry to match though.
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Old 28-08-2010, 12:03   #8
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Since about 30 years I have worked with computers, I have never heard things like that you are talking about.

In older days before the invention of the USB standard the computer have had a 9-pin or sometimes even a 25-pin serial connector which is connected to an UART chip on the motherboard. This we call here a real physical serial RS232 device.

Later on the serial connection was dropped and replaced by USB (abbreviation for Universal Serial Bus). So most computers have nowadays only USB connectors and even the Centronics printer connector (parallel port, 36-pins) was dropped.

So to connect a serial device to a modern computer you will need an USB/RS232 adapter which provides not a real physical com port but a virtual com port, usually in the range from com port number 4 and up. The com port numbers 1 to 3 are reserved to the real physical com ports and can't be used therefore. Responsible for creating the virtual com port is the USB driver of the USB/RS232 adapter. Any serial connection is limited to max. 115200 baud by the RS232 specs. And of course any created serial com port is seen in the device manager.

I hope this helps a little bit for understanding. For further and deeper information Wikipedia is a good source.
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Old 28-08-2010, 14:17   #9
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CarCode, your comments only serve to confuse an issue I was trying my best to explain. I am sorry you can't understand the difference between physical & virtual COM (serial) ports. Please read my post above again.

If it helps think of a USB derived COM port as a built in one such as those you refer to, commonly fitted to laptops ten years ago, but with an extra bit of wire connecting the same 9pin male dSub connector to the laptop via another serial device (USB). True it needs a driver dedicated to the adapter but in every respect it exists in a real & physical sense & is treated by the OS as such. The same applies to multiple adapters providing two, four or even eight COM ports from a single USB connection.

A virtual COM port has no physical manifestation but has an important use in allowing programs written to accept data from a physical COM port, to receive data from within the PC in a manner transparent to the program.

Typical applications would be in sharing a single external GPS feed - see GpsGate or the transfer of data from one program to another within the PC without any physical connection.
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Old 29-08-2010, 01:37   #10
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Try to read a little bit in Wikipedia about computing if you are confused.
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Old 29-08-2010, 02:15   #11
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Thanks for pointing that out. I have put a correction against the misplaced image in the Wiki article
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Old 29-08-2010, 08:37   #12
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richardhula is correct, a Serial-USB adapter is indeed a physical port - there is hardware involved, although it does require a specific device driver for the operating system. This is no different than video cards or any other bit of hardware - including the common BIOS ports, which every operating system can ship a driver for (i.e. it's common enough so drivers are provided already, and installing a separate driver is unnecessary).

A virtual port is one created entirely in software, with no hardware component.

Physical ports can be higher than COM1-4. Any driver, physical or virtual, can (whether or not it actually does) present a device as COM5 or higher.
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Old 29-08-2010, 09:06   #13
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scotte,
I am afraid you are wrong. There is no UART connected to the CPU when using an USB/RS232 converter. Same as a Bluetooth device which can use the SPP profile to provide a virtual com port to the system.
All these devices emulates RS232, but they are no real RS232. In fact USB or Bluetooth is only converted. That is all.
You may use a serial card with UARTs (available with more than 8 serial connectors) and attach the card to the PCI or ISA bus to have a real physical RS232. All other solutions are converters.
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Old 29-08-2010, 19:11   #14
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Sorry carcode but you are wrong. There is nothing about the RS232 spec that requires the use of a UART. I've implemented a dozen or more software/firmware UARTs on various mini/microprocessors.

Paul
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Old 30-08-2010, 01:01   #15
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We call this in our country a virtual com port. In your country it might be different.
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