Pls check the link below and have a look at tha application notes, sample codes etc.

Source code is not supported by Parallax, but is offered as a free download.

http://www.parallax.com/detail.asp?product_id=28146



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Features:

* Single-wire 4800 bps TTL Serial interface to BASIC Stamp, SX and Propeller microcontrollers.
* Provides either raw NMEA0183 strings or specific data, making it easier to use on the BASIC Stamp microcontrollers.
* Simple/raw mode selectable via I/O control.
* Single +5VDC supply @ 115 mA (typical)
* Standard 4-pin header interface (.100" spacing).