"Interface Protocols" is a complicated term for what is essentially the language of the input or output of the GPS unit. The Trimble Standard Interface Protocol (TSIP) is the native language for the Lassen LP GPS. TSIP is a binary language with a wide variety of commands and reports. TSIP reports can be output automatically, or they can be output as responses to queries. The format of the automatic reports can be easily configured. The receiver is factory configured for single precision Latitude-Longitude-Altitude. Report formats can be modified and position and velocity formats can be customized. The GPS unit sends the information (in the form of reports) it has gathered via the serial port. The output language is the format the information is received in.
This language is the most versatile, offering a large list of options that can be tacked onto the output. These options can be configured in TSIPCHAT, which will be discussed later. However, while its versatility is commendable, its format is also very hard to understand. Since this interface protocol was completely designed by the manufacturers, one must either learn the language, or use a different one (TAIP or NMEA). For simplicity, TAIP or NMEA 0183 is probably the easiest to understand, as well as use.
The Trimble ASCII Interface Protocol (TAIP) is a Trimble-specified digital communication interface based on printable ASCII characters over a serial data link. For most people, ASCII is much easier to understand than the more complicated TSIP language. The TAIP interface provides the means to configure the Lassen LP GPS receiver to output various TAIP sentences in response to query or on a scheduled basis. TAIP messages may be scheduled for output at a user specified rate starting on a given epoch from top of the hour.
The receiver can be configured to TAIP with the TSIPMonitor32 or TSIPCHAT programs contained in the Toolkit. The programs can be used to store these settings, along with all the other defaults, to non-volatile memory. As mentioned above, the receiver ports can also be set to TAIP through a TSIP port using TSIPCHAT and the TSIPCHAT program, or using TSIPMonitor32. Changing the language through the program TSIPMonitor32 is not advised, as the change is not permanent. Once the output language is changed, it merely changes right back again. However, through the program TSIPCHAT, one can change the characters of TSIP into the easy-to-understand TAIP language. However, TAIP has disadvantages as well. It only offers latitude, longitude, and altitude measurements. It does not offer ENU velocity.
The National Marine Electronics Association (NMEA) protocol is an industry standard data protocol which was developed for the marine industry. Trimble has chosen to adhere stringently to the NMEA 0183 data specification as published by the NMEA. NMEA data is output in standard ASCII sentence formats. Message identifiers are used to signify what data is contained in each sentence. Data fields are separated by commas within the NMEA sentence. In the Lassen LP GPS, NMEA is an output only protocol. This means commands must be entered through TSIPCHAT. This format is entirely in ASCII, so for the less experienced, it is much harder to read. However, it offers a little more flexiblity than TAIP in that it has customizable options.
Two default readings are provided with NMEA. The first is described as GGA, which is merely the GPS fix data. This is basically all the raw data the GPS unit collects. The second default is VTG, or ground speed. This can come in handy for the serious weather balloon hobbyists. There are 5 other customizable options, any of which can be turned on through TSIPCHAT. These include: GLL-or geographic position (latitude and longitude), GSA-or the GPS Dillution of Precision and active satellites, GSV-or GPS satellites in view, RMC-or recommended minimum specific GPS data, and finally ZDA-the time and date. This gives NMEA the leg up and may actually be more useful than TAIP. All these options can be shown in the next section under configuration.