Symmetricom XLi IEEE 1588 - Manual (Page 73)

XLi IEEE 1588 Clock 65
997-01510-03, Rev. C, 12/12/2006
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F69 – Time Mode
Use function F69 to select the time mode (time scale) shown or output by:
• The XLi’s front panel display
• The following command line functions (network and serial port):
- “F8 - Continuous Time Once-per-Second” on page 46
- “F9 - Time On Request” on page 49
• The CODE output on the Main CPU card. ( “F90 – Code Output Configuration” on page 78 )
• The PTP packets output by the IEEE 1588 card’s network port ( “F131 - Precision Time Protocol
Network Config” on page 119)
Select between the following time scales:
• TAI (International Atomic Time) is the basis for UTC and GPS time. TAI is the recommended
time scale for IEEE 1588 standard.
• UTC (Universal Coordinated Time) differs from GPS Time by the addition of leap-second
corrections to compensate for variations in the earth’s rotation.
• Standard Time is UTC plus a time zone adjustment. For example, Pacific Standard Time is UTC
minus 8 hours.
• GPS Time is derived directly from the GPS constellation and doesn’t contain any leap-second
adjustments or other GPS-to-UTC corrections.
• Local Time is UTC plus a time zone and a daylight saving time adjustment.
IMPORTANT interactions between F69 and the IEEE1588 card:
• When the IEEE 1588 card is operating as a PTP master, if F69 is set to TAI, Local, or GPS, the
1588 port outputs PTP with TAI time. 1
• When the IEEE 1588 card is operating as a PTP master, if F69 is set to Standard or UTC, the
1588 port outputs PTP with Standard or UTC time respectively.
• When the IEEE 1588 card is operating as a PTP slave, only TAI and GPS are valid settings for
F69. the reference source so can cause the XLi to output the incorrect time on the display, the
CODE output, F8, and F9. 2
• F69 has no effect on the IEEE 1588 card operating as a PTP slave. The IEEE 1588 card
operating as a PTP slave expects TAI from PTP.
The factory default for the XLi IEEE 1588 clock is TAI.
1. When F69 is configured for Local or GPS time, the display, the CODE output, F8, and F9 all output Local or GPS
time respectively. Only the IEEE 1588 card “redefines” Local and GPS from F69 as TAI.
2. The XLi requires the value of the offset between GPS and UTC in seconds to compute Local, Standard, and UTC
time. This offset can change by one second, and can potentially be updated at two times during the year. The XLi
typically obtains the offset from GPS while GPS is the primary reference source. The value of the offset isn’t
available from PTP should slave were the reference source). If a PTP slave is the reference source, a reference
source doesn’t obtain the offset from PTP and provide it to the XLi. If the PTP slave and GPS are both reference
sources, the value of offset is not reliable because.