Specifications

Operation 15
Operation
1PPS Out
By default, the receiver generates a TTL-level pulse every second within one
microsecond of the GPS time for synchronization of external equipment. Refer to
your individual receiver manual to determine signal location on the pinouts of the
ports. This pulse can be offset using the $PASHS,PPS command (refer to “PPS: Pulse
Per Second” on page 104). It can also synchronize either the rising edge (default) or
the falling edge to the GPS time. The receiver can generate this signal with a different
period (0.1 to 60 seconds). Setting the period to 0 disables the PPS pulse.
You may output the time tag of the pulse to a serial port via the
$PASHS,NME,PTT,c,ON (where c is the output port). This message will be sent
within 100ms of the pulse. It has been designed to minimize the latency when the
offset is 0.0 (within 30ms of the pulse when Fast CPD is off).
This output is driven by a 3.3 volt CMOS gate through a 150 ohm resistor, and is
intended to drive a high-impedance TTL or CMOS input. The minimum allowable
input resistance to guarantee TTL input levels is 250 ohms.
Data Output
Real time data output is only available through the four RS-232 ports. Refer to
Chapter 6 for more details. There are two types of messages:
• NMEA
NMEA is a standard data transfer format developed to permit ready and
satisfactory data communication between electronic marine instruments,
navigation equipment and communications equipment when interconnected
via an appropriate system. This is data in printable ASCII form and may
include information such as position, speed, depth, frequency allocation, etc.
Typical messages might be 20 to a maximum of 79 characters in length and
generally require transmission no more often than once per second.
Due to the extra resolution required for RTK operation, some NMEA messages are actually longer
than the specified 80 characters.
• Proprietary
When specific information was needed, and the NMEA standard did not
contain a suitable message, Ashtech created proprietary messages. Messages
are available in ASCII.
With the Fast Data output [F] option installed, the highest output rate supported is
10Hz. This is valid for every setting except for RTK Differential mode, if Fast CPD