User Manual

Trimble R6/R7 GPS and Trimble R8 GNSS Receivers User Guide 73
Event Marker Input and 1PPS Output 11
Trimble R7 GPS Receiver Operation
11.11PPS output
The Trimble R7 GPS receiver can output a one pulse per second (1PPS) time strobe
with an associated ASCII time tag output. The pulse is output through port 2 of the
receiver using the event marker/1PPS cable.
111.1 1PPS pulse definition
The leading edge of the pulse coincides with the beginning of each UTC second, as
shown in Figure 11.1. The pulse is driven by an RS-422 driver between nominal levels of
0 V and 4 V. The leading edge is positive, rising from 0 V to 4 V.
Figure 11.1 Time tag relation to 1PPS wave form
The pulse is approximately 8 μsec wide, with rise and fall times of about 100 nsec.
Resolution is approximately 40 nsec, but several external factors limit accuracy to
approximately ±1 μsec:
• Position errors, especially with user-entered reference. Each meter of error can
result in 3 nsec of error in the 1PPS pulse.
• Antenna cable length. Each meter of cable adds a delay of about 2 nsec to
satellite signals, and a corresponding delay in the 1PPS pulse.
111.2 ASCII time tag definition
Each time tag is output about 0.5 second before the corresponding pulse, as shown in
Figure 11.1. Time tags are in ASCII format on a user-selected serial port. The format of
a time tag is:
UTC yy.mm.dd hh:mm:ss ab
Where:
• UTC is fixed text.
• yy.mm.dd is the year, month, and date.
• hh:mm:ss is the hour (on a 24-hour clock), minute, and second. The time is in
UTC, not GPS time.
0V
4V
Seconds
Time tag output here Time tag applies here