REFERENCE MANUAL - FTP Directory Listing - Trimble

3 INTERFACE CHARACTERISTICS
Pulse-Per-Second (PPS)
The Copernicus GPS receiver provides a CMOS compatible TTL level Pulse-Per-
Second (PPS). The PPS is a positive pulse available on pin 19 of the Copernicus GPS
Receiver. The rising edge of the PPS pulse is synchronized with respect to UTC. The
timing accuracy is ±100 rms when valid position fixes are being reported.
The precise UTC or GPS time is reported in TSIP message 0x41 and NMEA message
EDA. The line reports are sent within 500ms after the corresponding PPS.
The rising edge of the pulse is typically less than 6 nanoseconds. The distributed
impedance of the attached signal line and input circuit can affect the pulse shape and
rise time. The PPS can drive a load up to 1mA without damaging the module. The
falling edge of the pulse should not be used.
The Copernicus' default PPS output mode is Always On, sometimes called or “Early
PPS”. In Always On mode, PPS is output immediately after main power is applied.
The PPS is driven by the Real Time Clock (RTC) until the receiver acquires GPS time
from the satellite and begins outputting fixes. In Always On mode, the PPS continues
even if the receiver loses GPS lock. The drift of the PPS, when the Copernicus GPS
receiver is not tracking satellites, is unspecified and should not be used for
synchronization.
The PPS output modes can be controlled with TSIP packet 0x35 and NMEA “PS”
Packet. The modes are Always On (default), Fix Based, or Always Off. Cable delay
compensation is available through the use of TSIP packet 0x8E-4A and NMEA “PS”
Packet. PPS pulse width is controlled by TSIP packet 0x8E-4F and the NMEA “PS”
Packet.
After a specific mode is selected, it can be stored in non-volatile memory (FLASH)
using TSIP command 0x8E-26.
Note – PPS can be configured as positive or negative polarity; factory default is
positive. The PPS pulse width is also configurable; factory default is 4.2
microseconds.
52 Copernicus GPS Receiver