Trimble Outdoors SK8 - Manual (Page 50)

3-8 Lassen-SK8 Embedded GPS Module
Software Interface
The following two known issues for previous versions of receivers exist as a result of
testing a representative sample of Trimble OEM receivers.
• An almanac recorded prior to WNRO is not correct after WNRO. This problem
only exists when the receiver main power is OFF and battery back-up power is
ON at the moment of WNRO. Once the receiver is cold started, a post-WNRO
almanac is collected and the receivers behavior returns to normal.
• Day-month-year representations will be incorrect after WNRO when using
specific TAIP and NMEA messages. Time and day information will not be
effected however.
There is no impact for TSIP users on position or time information. The reported GPS week
number will reset to zero however, and users that require this information may need to
make a software modification to accommodate this change.
ACE GPS/Palisade Family Firmware Version 7.xx Software Modifications
The Lassen-SK8 receiver has been designed to handle WNRO and there are no problems
with either dates or the first fix after WNRO through the year 2015.
I
Caution – Trimble OEM GPS receivers have reported the true GPS Week Number in
TSIP messages 0x41 and 0x8F-20 as a number between 0 and 1023. The Lassen-SK8
however, outputs the Extended GPS Week Number as the absolute number of weeks
since the beginning of GPS time or 06 January 1980. If the true GPS Week Number is
desired, the system developer should ignore the extra MSBs of the Extended GPS Week
Number and use only the 10 LSBs.
3.6 Differential GPS
The Lassen-SK8 module can use differential corrections to compute a Differential GPS
position (DGPS). DGPS can provide position accuracy of 2 meters (1 sigma).
RTCM SC-104, the industry standard format for differential corrections, is available from
most DGPS reference stations, Coast Guard beacon transmissions, and commercial DGPS
subscription services. The Lassen-SK8 is fully compatible with RTCM SC-104 Version
2.1. The Lassen-SK8 is configured to accept RTCM SC-104 correction data over port 2
(J4, pin 7) at 4800 baud, 8 data bits, 1 stop bit and no parity. The DGPS operating mode is
set to Automatic which means that the receiver will provide differential GPS solutions
when valid correction data is available and will output standard GPS solutions when no
valid correction data is available.
No setup is required to use RTCM SC-104 differential corrections, however, you may
need to reconfigure the serial port characteristics (baud rate, data bits, stop bits and parity)
to match the characteristics of your RTCM SC-104 data source using the TSIP packet
BCh. See Appendix A for more information on this message. Table 3-1 summarizes the
default characteristics for the Lassen-SK8 serial ports.