NAVIOR-24S
™
CHAPTER IV
Operation and Performance
65
NAVIOR-24S ™
Revision
V1.00 20.05.2008
Pulse-Per-Second (PPS)
The NAVIOR-24S GPS/GLONASS receiver provides a four microsecond wide, CMOS compatible
TTL level Pulse-Per-Second (PPS). The PPS is a positive pulse available on pin 4 of the NAVIOR-
24S GPS/GLONASS receiver power and I/O connector. The rising edge of the PPS pulse is
synchronized with respect to GPS. The timing accuracy is ±50 nanoseconds when valid position
fixes are being reported.
The rising edge of the pulse is typically less than 20 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 8mA without damaging the module. The falling edge of the pulse should not be used.
The PPS is always on (early PPS) and is driven by the Real Time Clock (RTC) until the receiver
acquires GPS time from the satellite and is obtaining fixes. The PPS is output immediately after
main power is applied, and continues even if the receiver loses GPS lock. The drift of the PPS,
when the NAVIOR-24S GPS/GLONASS receiver is not tracking satellites, is unspecified and
should not be used for synchronization.
PPS Output Mode
PPS output mode can be controlled by BINR command packet D7h. The following PPS modes are
supported.
Always Off
When the Always Off mode is selected, the PPS output remains low at all times. Disabling the PPS
output has no affect on normal receiver operations, and position fixes are calculated as usual. This
mode can be selected at any time during receiver operation. The PPS output is immediately
switched off (disabled) when the BINR command for this mode is received.
Always On (default)
When the PPS output is configured for Always On (early PPS), it is driven by the Real Time Clock
(RTC) until the receiver acquires GPS time is generating position fixes. In this mode, the PPS
output continues even if the receiver loses GPS tracking. The maximum drift of the PPS pulse is
when not tracking satellites could be quite large, therefore the PPS output should not be used for
precise synchronization when no position fix occurs. The PPS can be switched to Always On mode
any time during normal operation. This mode is the factory default setting.
Fix Based
In this mode, the PPS output is turned on only while fixes are taking place. If the receiver is not
tracking satellites, the PPS output is turned off until the signals are required and position fixes are
valid again. If the receiver is switched from Always On to Fix Mode, and the receiver has not yet
started generating position fixes, the PPS output will turn off until a new fix is obtained.