10: Applications and Hints
GNSS Receiver Module A5135-H User Guide
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SRAM is backed with the typical current of 20 μA drawn from Vcc. To wake the mod-
ule up again, toggling the ON_OFF to HIGH.
10.6 Extended Ephemeris
The receiver can support two versions of using Extended Ephemeris (EE) data. The
first one is the version, where the EE data are calculated on a server, are transmitted
to device incorporating the receiver, and are then loaded into the receiver. These
data can be valid for up to seven days.
The second version is the internal extrapolation of available “natural” Ephemeris data.
This is done automatically and no external support is required. The internally calcu-
lated EE data are valid for up to 3 days.
The receiver firmware will define which set of EE data to use or will neglect those in
case “natural” data are available. Both versions of EE data will help to further lower
power consumption in SiRFaware
TM
mode.
10.7 TM_GPIO5 pin (1 pulse per second pin)
The 1PPS pin is an output pin.
In addition to precise positioning, GPS+GLONASS also allows for accurate timing
due to the synchronized atomic clocks in the GPS+GLONASS satellites. While the
current date and time is transmitted in NMEA sentences (UTC), an exact and accu-
rate timing signal is provided via the 1PPS pin of the A5135-H GPS+GLONASS re-
ceiver.
Under good signal conditions the 1PPS signal comes between 620ns and 710ns after
the full GPS+GLONASS system second which is accurately (around 10ns) synchro-
nized to UTC. Therefore the 1 second clock can be derived and maintained within
around 90ns under good signal conditions.
Note:
The 1PPS clock accuracy directly depends on the position accuracy!
The GPS+GLONASS signals travel at the speed of light, therefore a position inac-
curacy directly translates into 1PPS inaccuracies.
10m position deviation ≈ 33ns 1PPS deviation (typically)
100m position deviation ≈ 333ns 1PPS deviation (typically)
The NMEA messages containing absolute timing information (UTC time) are pro-
vided around 300ms after the 1PPS signal typically. This may change with the
GPS+GLONASS receiver setup.
The 1PPS signal is provided on a “as is” basis with no accuracy specification. It’s
NOT recommended to use 1PPS signal for accurate timing application. The given
values are based on a 10 satellite, static GPS+GLONASS simulator scenario.