The SL869-T timing module is a member of the SL869 product family that is intended for use
in timing applications. The timing firmware within the module provides an accurate PPS
signal by holding an internal reference position that represents the location of the antenna for
the timing module, and then by applying satellite measurements only to the calculation of
time. Because the internal reference position is “held” by the module firmware, this timing
feature of the SL869-T is also known as
Position
Hold
mode. While in Position Hold mode,
the SL869-T timing module firmware also performs time-receiver autonomous integrity
monitoring (T-RAIM) to ensure a high degree of integrity of the PPS signal. Position Hold
mode and the held internal reference position are maintained through commanded software
resets.
The serial communication interface between the SL869-T timing module and the Host
processor is based on the NMEA-0183 protocol standard. More information regarding the
NMEA protocol and its use by the SL869 module family can be found in Section 2 of the
Software Guides for public and authorized users listed as References in the Introduction
above. Note that the default settings for the serial communications port used by the SL869-T
timing firmware are:
115200 Baud
Eight data bits
No parity bits
One stop bit
The timing feature is managed using proprietary NMEA commands and messages. A
command interface allows the user to set and poll the internal reference position used for
Position Hold mode, as well to obtain information regarding the status of the T-RAIM
algorithm.
Unlike the standard SL869 module, by default the SL869-T timing module outputs a pulse
every second. It is able to output an accurate pulse with only one satellite in track when in
Position Hold mode.
As mentioned above, in Position Hold mode an internal reference position is held by the
SL869-T timing module firmware, which removes position uncertainty and allows the
firmware to apply satellite measurements exclusively to the calculation of time and the
