u-blox ANTARIS 4, Руководство по системной интеграции

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D.6 Migration from TIM-ST to TIM-4x
Migrating a TIM-ST design to one of the TIM-4x GPS receivers is usually an easy, straightforward procedure. This
section summarizes most important differences.
NMEA Protocol
TIM-ST and TIM-Lx output NMEA data (GGA, GLL, GSA, GSV, RMC, VTG and ZDA messages) on port 1.
TIM-ST TIM-4x (ANTARIS
®
4) Remarks
NMEA V2.2 NMEA V2.3 Most NMEA parsers should be able to handle V2.2 and V2.3. Should your
parser struggle with V2.3, configure TIM-4x to output NMEA V2.1 by sending
an UBX-CFG-NMEA message.
12 channels 16 channels ANTARIS
®
4 is able to track up to 16 satellites in parallel. Since one GSV
message contains only up to 4 satellites, ANTARIS may send up to 4 GSV
messages whereas TIM-ST only output 3. If this causes problem, reduce the
NMEA output of ANTARIS to 12 satellites by sending a CFG-NMEA message
Lat and Long are output in Lat and Long are only ANTARIS 4 can be reconfigured to output Lat and Long in case of invalid fixes
case of invalid fixes output for valid fixes
®
by sending an UBX-CFG-NMEA message.
Accepts position up to a Accepts position up to a ANTARIS
PDOP of 50 PDOP of 25 conservative approach with a PDOP of 25 works usually fine. However, it’s
possible to configure TIIM-Lx to accept position with a higher PDOP by sendin
®
4 receivers are more sensitive than TIM-ST. Hence the more
g
a UBX-CFG-NAV2 message
Lat and Long are output
with 4, the time with 3
Lat and Long are output
with 5, the time with 2
The NMEA specification is fairly open and allows minor variations in the
implementation (e.g. number of position after decimal point, etc.) but it always
number of digits for the individual message fields. It will even be able to handle
empty fields ",,". Beside the commas, a good parser should be able the handle
no
T
position after decimal point position after decimal point requests commas between as a separator between NMEA data fields. One
should therefore write a parser that searches for commas and extracts
everything between two commas. This way, the parser is independent of the
the valid flags correctly. Data are only valid if the valid flag is set to valid. If it’s
set to invalid, the NMEA parser should reject data output by the receiver. By
means should it forward it to the application.
Starting with Firmware 5.0, it’s possible to configure ANTARIS
®
4 to output LA
& LON with 4 digits etc.
Supports proprietary NMEA Supports proprietary NMEA The NMEA specification does not include input messages. This is why GPS
messages (PSRF) messages (PUBX) manufacturers introduce proprietary NMEA messages. If PSRF messages have
been used with TIM-ST, migrate them to either PUBX or even better to UBX-
CFG-xxx messages. The latter is preferred and it’s easy since ANTARIS is able to
handle to protocols on the same port (4.3).
Binary Protocol
TIM-ST supports SiRF binary protocol whereas TIM-4x supports UBX protocol. These two protocols are not
TIM-ST does not have a built-in antenna supervisor whereas all TIM-4x modules have a built-in short-circuit
compatible. It is necessary to migrate the host software to UBX protocol if SiRF binary was used before.
Antenna and Antenna Supervisor
detection. TIM-ST designs with external active antenna supervisor will not work without minor modifications to
the circuitry.
Power Supply
TIM-4x receivers consume approximately 120mA less current, which is usually not a problem.
TIM-ST TIM-4x (ANTARIS
®
4) Remarks
Vcc 2.75 – 3.45 2.7 – 3.3V
Current Consumption <160mA Approx 36 – 40mA TIM-4x current consumption depends on TIM-4x variant
Power Saving Mode TPM, Push-2-fix FixNOW In most cases, it’s not necessary to use FixNOW mode due to
much lower current consumption of TIM-4x
the
Note: Make sure the ripple on Vcc is below 50mV.
GPS Modules - System Integration Manual (SIM) (incl. Reference Design) Migration to ANTARISP®P4 receivers
GPS.G4-MS4-05007-A1 Page 173