Tyco Electronics A1029, Руководство пользователя

Страница: 36 / 43

GPS Receivers A1029
Page 36 of 43 User’s Manual V3.2 - 02/06
11.4 VANT pin (antenna voltage input pin)
The VANT pin is an input pin.
The supply voltage for an active GPS antenna has to be fed into the Vant pin.
The easiest way to do that is to connect Vcc to VANT. The maximum current is
50mA. Therefore, when connected to Vcc a current limiter should be used.
11.5 LOCK pin (position fix pin)
The LOCK pin is an output pin.
When there is no valid position fix, the signal on the pin will be a continuous logic
low. During a valid position fix phase, the output signal will be a continuous logic
high.
11.6 ENABLE pin (low-power mode)
The ENABLE pin is an input pin.
For enabling normal operation of the module, the pin has to be on HIGH level (e.g.
connected to Vcc). When the ENABLE pin is pulled down to GND, the module will
go to a low power mode where only the RTC will be supported (if a power source is
still connected to Vcc). I.e. date and time will be valid after wake-up. The current
draw will fall from typically 50mA to typically 30µA. Do not pull down low nRST at
the same time! This is not necessary and will result in additional current draw!
11.7 1PPS pin (1 pulse per second pin)
The 1PPS pin is an output pin.
In addition to precise positioning, GPS also allows for accurate timing due to the
synchronized atomic clocks in the GPS satellites. While the current date and time is
transmitted in NMEA sentences, an exact and accurate timing signal is provided via
the 1PPS pin of the A1029 modules.
The 1PPS signal is valid only, whenever the GPS modules provide a valid position
fix. Therefore it is recommended to monitor the LOCK signal in parallel (or logically
AND the 1PPS and LOCK signals).
The rising edge of the signal is synchronized to GPS time and therefore also to
UTC. The 1PPS signal is characterized (a) by the delay “d” between the start of a
GPS second and the rising edge of the 1PPS and (b) by standard deviation of this
delay providing a measure for the stability or jitter of this signal. Additionally, the
duration “l” of the signal is outlined.