[aprssig] Com port SHARING vs Com Port JOINING
Stephen H. Smith
wa8lmf2 at aol.com
Mon Jan 14 21:27:35 CST 2008
Claude Head III wrote:
> I seem to remember comments on this SIG some time ago about a COM port
> sharing utility, whereby a single COM port could be used by two (or
> more) applications at the same time.
> My desire here is to use a Garmin GPS receiver to feed data to a
> DeLorme Street Atlas program and at the same time feed the GPS data to
> a program that would keep the computer (a Dell Latitude laptop) time
> correct. I have found an inexpensive program that will set the
> computer's time using GPS data, but it does not share access to the
> COM port.
The various replies to this question are confusing two different issues:
1) Joining two applications (running at the same time on the same
PC) that each normally communicate with hardware via com ports. For
example, MixW operating as a software TNC outputs to a virtual serial
port. You then want to connect the virtual TNC to an application, such
as UIview that expects to connect to a real TNC connected to a serial
port. Port bridge utilities such as the MixW serial port bridge create
a pair of simulated serial ports cross-connected (i.e. virtual null
modem). Each application is then set to use one of the virtual ports.
The net effect is the same as connecting two REAL serial ports on the
same PC back-to-back with a null-modem cable, without wasting the
precious physical ports on data that never leaves the machine.
2) Spitting a single data stream from an external hardware device
such as a GPS into multiple virtual serial ports so that several mapping
(or APRS) programs can use the GPS data at the same time. The
Comfoolery application can do this but is rather kludgy since you have
to run TWO programs back-to-back to implement the splitter; then run
multiple applications at the same time to use the ports.
The best application for splitting ports is GPSgate from Franson Software.
This utility can split the incoming data stream from either a physical
serial port or a virtual com port created by a USB-to-serial dongle into
almost any number of virtual com ports that other programs can then use.
It can also convert to/from TCP/IP so that a com port source can be
distributed over a LAN via TCP/IP. On other PCs on the lan, copies of
GPSgate can then convert TCP/IP back to virtual com ports.
In addition, GPSgate can convert Garmin proprietary binary format coming
in on USB, to standard ASCII NMEA on multiple virtual com ports! This
allows you to use just about any Garmin GPS, even those without NMEA
and/or serial outputs, with almost any program that can use standard
serial NMEA data.
GPSgate is available in two versions. A lite "Express" version that
spits a single input, real or virtual, into just two virtual outputs is
USD $13. The "Standard" version that can split multiple source ports
into any number of outputs is USD $40. If you "split" a virtual
comport into just one new port, you can create the equivalent of the
1-port-to-1-port bridge utilities described in 1) above.
You can run multiple instances of GPSgate Standard on a single machine.
For example, you could have one instance splitting a GPS from a physical
port for use with multiple mapping programs. At the same time, a second
instance could be joining a soundcard soft TNC to an APRS application
like UIview or APRSplus.
Real world applications that I have used:
I routinely split the single physical COM port on my Panasonic Toughbook
mobile laptop to feed GPS data into UIview, Visual GPS, MapPoint,
Delorme Topo USA, and Precision Mapping at the same time. GPSgate is
set to load automatically each time the computer boots.
Using a second instance of GPSgate on the same laptop, I have
intercepted one output of the first instance and converted to TCP/IP. I
then distributed the IP NMEA stream via ad-hoc WiFi to a second copy of
GPSgate running on a second laptop in the back seat of the car, where
several more mapping apps were running.
Stephen H. Smith wa8lmf (at) aol.com
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